Declining male births with increasing geographical latitude in Europe

Ambient temperature-related sex ratio at birth in historical urban populations: the example of the city of Poznań, 1848-1900

This study examines whether exposure to ambient temperature in nineteenth-century urban space affected the ratio of boys to girls at birth. Furthermore, we investigate the details of temperature effects timing upon sex ratio at birth. The research included 66,009 individual births, aggregated in subsequent months of births for the years 1847-1900, i.e. 33,922 boys and 32,087 girls. The statistical modelling of the probability of a girl being born is based on logistic GAM with penalized splines and automatically selected complexity. Our research emphasizes the significant effect of temperature in the year of conception: the higher the temperature was, the smaller probability of a girl being born was observed. There were also several significant temperature lags before conception and during pregnancy. Our findings indicate that in the past, ambient temperature, similar to psychological stress, hunger, malnutrition, and social and economic factors, influenced the viability of a foetus. Research on the effects of climate on the sex ratio in historical populations may allow for a better understanding of the relationship between environmental factors and reproduction, especially concerning historical populations since due to some cultural limitations, they were more prone to stronger environmental stressors than currently.

The role of maternal preconception vitamin D status in human offspring sex ratio

Evolutionary theory suggests that some animal species may experience shifts in their offspring sex ratio in response to maternal health and environmental conditions, and in some unfavorable conditions, females may be less likely to bear sons. Experimental data in both animals and humans indicate that maternal inflammation may disproportionately impact the viability of male conceptuses; however, it is unknown whether other factors associated with both pregnancy and inflammation, such as vitamin D status, are associated with the offspring sex ratio. Here, we show that among 1,228 women attempting pregnancy, preconception 25-hydroxyvitamin D concentrations are positively associated with the live birth of a male infant, with notably stronger associations among women with elevated high sensitivity C-reactive protein, a marker of systemic low-grade inflammation. Our findings suggest that vitamin D may mitigate maternal inflammation that would otherwise be detrimental to the implantation or survival of male conceptuses in utero.

A systematic search of the factors that influence the sex ratio at birth

INTRODUCTION

The sex ratio at birth has been studied for decades. A systematic review of the factors that influence this has never been performed. This study conducted a systematic search of this topic.

METHODS

A scoping review of the literature was initially carried out in January 2012 and this was formally updated for contemporaneity in December 2017. A systematic search of the literature subsequently followed in May 2019 and was conducted based on PRISMA statement's flow diagram. The search was applied across five databases: Cumulative Index to Nursing and Allied Health Literature (CINAHL), MEDLINE, PubMed, The Cochrane Library and Web of Science and was restricted to January 1, 1990 to May 31, 2019. The systematic review stopped at screening stage of the PRISMA. A narrative approach was adopted to report study findings.

RESULTS

494 studies were included. Ten factors were identified from the literature as having an influence on M/F, with stress and sex-selective termination being the most predominant. Additional factors included the hormonal theory, geographical trends, coital rates, radiation, secular trends, seasonality and theoretical modeling.

DISCUSSION

Future studies addressing M/F should adopt similar methodologies in order to provide the possibility of comparison between findings and a more formal form of systematic review.

MATERNAL THYROID-STIMULATING HORMONE LEVEL IN THE FIRST TRIMESTER AND SEX RATIO AT BIRTH

Objective: Few studies have explored the influence of thyroid status on sex ratio at birth, and conclusions are inconsistent. The aim of this study was to determine if there is an association between serum thyroid-stimulating hormone (TSH) level in first trimester and sex ratio at birth. Methods: The study was a retrospective cohort study performed at a tertiary care center. From March 2014 to February 2017, a total of 4,822 women who had thyroid function testing during the first trimester were included. Study population was divided into five groups according to quintile of TSH level (≤0.60 mIU/L; 0.61 to 1.02 mIU/L; 1.03 to 1.44 mIU/L; 1.45 to 2.13 mIU/L; and ≥2.14 mIU/L). Logistic regression analysis was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) of the percentage of male infants across the quintiles, with the lowest quintile as the reference category. Results: Median level of TSH was 1.27 mIU/L in women who delivered a boy, which was significantly higher than that in women who delivered a girl (1.15 mIU/L). After adjusting for age, gravidity, and parity, multivariate logistic analysis found that women in quintiles 3, 4, and 5 all showed significantly higher ORs for delivering a boy than those in quintile 1. In addition, after adjusting for age, gravidity, and parity, serum TSH was significantly associated with likelihood of having a boy (OR, 1.08; 95% CI, 1.03 to 1.13). Conclusion: Maternal TSH level in the first trimester is positively associated with the probability of delivering a male newborn. Abbreviations: CI = confidence interval; FT3 = free triiodothyronine; FT4 = free thyroxine; OR = odd ratio; SRB = sex ratio at birth; TBG = thyroxin-binding globulin; TSH = thyroid-stimulating hormone.

Write a Scientific Paper (WASP) - What can I publish [1]? Types of studies

As an experienced writer, one is often asked the question "what can I publish" by younger and inexperienced colleagues who must publish. This paper will briefly review the reasons why academics publish and will then outline what kind of papers one may be able to publish with relative ease, using personal experience and citing first hand material as a practical guide. Potential authors must cultivate "a lean and hungry look" as competition from fellow writers is stiff, and editors are choosy. However, do take heart - if we, older colleagues did and can, you can too.

Sex ratio at birth is associated with type 1 diabetes characteristics

AIMS

To assess the association between maternal diabetes characteristics and sex ratio at birth (SRB) in women with type 1 diabetes mellitus.

METHODS

We performed a case-control study. The study subjects were infants born alive to women with type 1 diabetes and singleton pregnancies. Cases and controls were defined as male and female newborns, respectively. SRB was analysed according to diabetes-related characteristics adjusting in a logistic regression analysis for maternal characteristics known to affect SRB in the general population.

RESULTS

The observed SRB (238 males/468 live births = 0.509) did not differ from the expected. In the logistic regression analysis, SRB was significantly associated with three diabetes characteristics: (1) diabetes duration, with odds ratios (ORs) for a live male newborn = 1.22 (95 % confidence interval (CI), 0.66-2.24 for ≤5 years, OR 2.79 (95 % CI 1.36-5.74) for >20 years; (2) mean first-trimester glycated haemoglobin, with OR 1.98 (95 % CI 1.09-3.62) for ≤6.7 % (50 mmol/mol) and OR 2.61 (95 % CI 1.16-5.85) for >8.2 % (66 mmol/mol) and (3) mean first-trimester insulin dose, with OR 0.70 (95 % CI 0.36-1.38) for ≤0.5 IU/kg/day and OR 0.18 (95 % CI 0.05-0.59) for >1.0 IU/kg/day.

CONCLUSIONS

We conclude that SRB in this cohort is independently associated with three diabetes characteristics. These associations are to be confirmed.

Couples' urinary concentrations of benzophenone-type ultraviolet filters and the secondary sex ratio

The secondary sex ratio (SSR), defined as the ratio of males to females at birth, has been investigated in relation to endocrine disruptors to search for environmental toxicants perturbing human sex selection. Benzophenone (BP)-type ultraviolet (UV) filters, which are used in sunscreens and personal care products, have been reported to exert estrogenic and anti-androgenic activities. This study aimed to evaluate the association between maternal, paternal, and couple urinary concentrations of BP-type UV filters and the SSR, given the absence of previous investigation. The study cohort comprised 220 couples who were enrolled in the Longitudinal Investigation of Fertility and the Environment (LIFE) Study between 2005 and 2009 prior to conception and who had a singleton birth during the follow-up period. Couples' urinary concentrations of five BP-type UV filters (ng/mL) were measured using triple-quadrupole tandem mass spectrometry: 2,4-dihydroxybenzophenone (BP-1), 2,2',4,4'-tetrahydroxybenzophenone (BP-2), 2-hydroxy-4-methoxybenzophenone (BP-3), 2,2'-dihydroxy-4-methoxybenzophenone (BP-8), and 4-hydroxybenzophenone (4-OH-BP). Modified Poisson regression models were used to estimate the relative risks (RRs) of a male birth for each BP-type UV filter, after adjusting for potential confounders. When maternal and paternal urinary BP-type UV filter concentrations were modeled jointly, both maternal BP-2 (2nd vs 1st tertile, RR, 0.62, 95% confidence interval [CI], 0.43-0.91) and paternal BP-2 (3rd vs 1st tertile, RR, 0.67, 95% CI, 0.45-0.99; p-trend, 0.04) were significantly associated with an excess of female births. Contrarily, maternal 4-OH-BP was significantly associated with an excess of male births (2nd vs 1st tertile, RR, 1.87, 95% CI, 1.27-2.74; 3rd vs 1st tertile, RR, 1.80, 95% CI, 1.13-2.87; p-trend, 0.02). Our findings provide the first evidence suggesting that BP-type UV filters may affect the SSR. However, future corroboration is needed, given the exploratory design of this study.

Secular trends in newborn sex ratios

A wide variety of factors have been shown to influence the male to female ratio at birth, which invariably displays a male excess. This paper will review and amplify recent work by the author, with specific references to individual countries, regions and entire continents in order to provide a global overview of this subject. It will be shown that stress, including stress related to political events, influences this ratio. Man-made radiation is also shown to have played a significant role in relation to the Windscale fire (1957) and Chernobyl (1986).

Climate change is associated with male:female ratios of fetal deaths and newborn infants in Japan

OBJECTIVE

To evaluate whether climate change is associated with male:female ratios (sex ratios) of fetal deaths and births in Japan.

DESIGN

A population-based cohort study.

SETTING

Not applicable.

PATIENT(S)

Newborn infants and fetuses spontaneously aborted after 12 weeks of gestation.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Yearly sex ratios of fetal deaths and newborn infants and monthly fetal death rates and sex ratios of newborn infants.

RESULT(S)

A statistically significant positive association was found between yearly temperature differences and sex ratios of fetal deaths; a statistically significant negative association was found between temperature differences and sex ratios of newborn infants from 1968 to 2012, and between sex ratios of births and of fetal deaths. The sex ratios of fetal deaths have been increasing steadily along with temperature differences, whereas the sex ratios of newborn infants have been decreasing since the 1970s. Two climate extremes, a very hot summer in 2010 and a very cold winter in January 2011, showed not only statistically significant declines in sex ratios of newborn infants 9 months later in June 2011 and October 2011 but also statistically significant increases of fetal death rates immediately, in September 2010 and January 2011.

CONCLUSION(S)

The recent temperature fluctuations in Japan seem to be linked to a lower male:female sex ratio of newborn infants, partly via increased male fetal deaths. Male concepti seem to be especially vulnerable to external stress factors, including climate changes.

Sex ratio at birth is associated with first-trimester maternal thyrotropin in women receiving levothyroxine

BACKGROUND

The sex ratio at birth (male out of total alive newborns) is historically established at 0.515 and is influenced by numerous factors. It is not known, however, whether it is influenced by maternal thyroid conditions. Our aim was to analyze its association with maternal thyroid autoimmunity and first-trimester thyrotropin (TSH).

METHODS

We performed a retrospective cohort study at a tertiary care center. We studied 167 women who had received pregestational treatment with levothyroxine for hypothyroidism or differentiated thyroid carcinoma and gave birth to live infants. Women with secondary/tertiary hypothyroidism, pregestational diabetes mellitus, or multiple pregnancies were excluded. Autoimmunity was defined as present/absent, and mean first-trimester TSH was tested both as a quantitative variable and using six predefined categories. The outcome measure was sex ratio at birth.

RESULTS

The sex ratio at birth was 0.485, not significantly different from expected. Maternal characteristics were similar in mothers of female and male newborns with the exception of mean first-trimester TSH, which was higher in pregnancies of female fetuses (3.27 vs. 2.52 mUI/L, p<0.025). Newborn sex differed across predefined TSH categories (p<0.021, with a sex ratio of 0.200 [95% confidence interval 0.00-0.402] for TSH ≥10 mUI/L). A multiple logistic regression analysis to predict newborn male sex confirmed maternal mean first-trimester TSH as the single predictor (odds ratio 0.900 [95% confidence interval 0.823-0.984], p<0.020).

CONCLUSIONS

In women under pregestational treatment with levothyroxine, mean maternal first-trimester TSH is negatively associated with sex ratio at birth. This association has not been previously described.

Secular trends and latitude gradients in the male-female ratio at birth in Yugoslavia and the ex-Yugoslavian States

BACKGROUND

Latitude gradients and secular trends in Europe and North America have been found in the male-female ratio at birth (M/F: male births divided by total births) which approximates 0.515.

METHODS

Annual national data for Yugoslavia and the post-Yugoslavia States for male and female live births were obtained from the World Health Organisation and analysed with contingency tables.

RESULTS

This study analysed 22,020,729 live births. There was a increasing trend in M/F prior to the breakup of the former Yugoslavia (1950-1990, p = 0.002), followed by a decreasing trend after 1990 (p = 0.02). A latitude gradient was also noted, with more males being born in southern, warmer latitudes (p < 0.0001). There was an overall excess of 42,753 male births based on an anticipated M/F of 0.515.

CONCLUSION

M/F is decreasing in this region, similar to the rest of Europe and North America. A latitude gradient is also present with more males being born in warmer (more Southern) latitudes (p < 0.0001), even in this small region and over the short time-frame studied.

Secular trends in sex ratios at birth in South America over the second half of the 20(th) century

OBJECTIVES

Latitude gradients have been found in the male-female ratio at birth (M/F: male divided by total births), which is anticipated to be 0.515.

METHODS

Annual national male and female live births by country were obtained for South America from the World Health Organization (WHO) and analysed with contingency tables. The continent was arbitrarily divided into two regions: a region 10° above the Equator to 20° below the Equator, and a second area 20° below the Equator.

RESULTS

This study analyzed 147,773,689 live births. An overall increasing trend in M/F was found for the region >20° (p<0.0001) for the entire period. For the aggregate, a significant decrease was present for the period 1950-74 (p = 0.01) followed by a significant increase thereafter (p<0.001). A latitude gradient was also noted, with more males being born in cooler (more Southern > 20° S) latitudes (p<0.0001). There were 3,765,648 male births in excess of what was anticipated.

CONCLUSION

The M/F ratio is increasing in South America, unlike the decline present in Europe and North America. This study also showed that M/F latitude gradients are similar to those previously reported in North America, with more males being born in cooler latitudes, contrary to the trends reported in Europe. The interplay of several poorly understood factors is likely.

Sex ratios at birth in the British Isles over the past sixty years

The male-female ratio at birth (M/F: male births divided by total births) is anticipated to approximate 0.515. This has been shown to be declining in industrialised countries and to be displaying a latitude gradient in Europe, with more males born in warmer, southern climates. Annual national data for the British Isles for male and female live births were obtained from the World Health Organization and analysed with contingency tables. Analysis was performed separately for individual countries and for totals for the northern (Scotland and Northern Ireland) and southern (England and Wales, and the Republic of Ireland) regions. This study analysed 49,263,493 live births. There was an overall rise in M/F up to the late 1970s, followed by a decline thereafter. The step-down for the periods of 1975-1979 to 1980-1984 was highly significant for both the northern (p = 0.001) and southern regions (p < 0.0001). An overall decreasing trend in M/F was noted (p = 0.04) which reversed the expected European latitude gradient. More males are born in Scotland and Northern Ireland than in England and Wales, and the Republic of Ireland (p = 0.02). There was a male deficit of 59,311 live births.

CONCLUSION

M/F is decreasing in the British Isles, to the south more than to the north, to the extent that the expected latitude gradient is reversed. The interplay of several poorly understood factors is likely.

Secular trends and latitude gradients in sex ratio at birth in Asia during the past 60 years

BACKGROUND

Latitude gradients and secular trends in Europe and North America have been found in the male-female ratio at birth (M/F: male births divided by total births), which is anticipated to approximate 0.515.

METHODS

Annual national data for Asian countries for male and female live births were obtained from the World Health Organization and analyzed with contingency tables.

RESULTS

A total of 245,938,211 live births were analyzed. An overall increasing trend in M/F was found (P < 0.0001). A latitude gradient was also noted, with more boys being born in southern, warmer latitudes (P < 0.0001). There was an overall deficit of 1,351,757 male births based on an anticipated M/F of approximately 0.515.

CONCLUSION

M/F is increasing overall in Asia, unlike the decline previously noted in Europe and North America. Moreover, it had been shown that there is a higher incidence of male births in southern Europe than in the north, with the opposite gradient in North America. This paper shows that M/F latitude gradients in Asia are in keeping with those of Europe. The overall M/F in Asia may be rising due to improving socioeconomic conditions, and the interplay of several poorly understood factors is likely.

Secular trends and latitude gradients in sex ratios at birth in Czechoslovakia and the post-Czechoslovakian states

Latitude gradients and secular trends in Europe and North America have been found in the male-female ratio at birth (M/F: male births divided by total births) which is expected to be 0.515. Annual national data for Czechoslovakia and the post-Czechoslovakian (Czech Republic and Slovakia) countries for male and female live births were obtained from the World Health Organisation and analysed with contingency tables. This study analysed 13,123,538 live births. An overall decreasing trend in M/F was found (p < 00001). No latitude gradient was noted. There was an overall deficit of 15,232 male births based on an M/F of 0.515. M/F is declining in this region, despite well developing economies that have resisted the worldwide slowdown. An interplay of several poorly understood factors is likely.

Secular trends and latitude gradients in sex ratios at birth in the former Soviet Republics

BACKGROUND

The male-female ratio at birth (M/F: male births divided by total births), which is anticipated to approximate 0.515, has been shown to exhibit latitude gradients and secular trends.

METHODS

Annual national data for male and female live births for the 15 countries that comprise the former Soviet Union were obtained from the World Health Organisation for the period 1980-2009 (115,167,569 total live births) and analysed with contingency tables. Spearman correlation was also carried out to compare percentage annual gross domestic product growth (GDP%--downloaded from the World Bank) and M/F. In this context, GDP% is used as a measure for economic hardship or wellbeing within the populace.

RESULTS

There have been overall highly significant secular increases in M/F (p < 0.0001) in the countries and regions investigated. M/F is significantly lower in the three more northern regions (Russian Federation, Baltic States and Central Asia. M/F 0.51324, 0.51335-0.51314) than the two more southern regions (Southern Caucasus and Eastern Europe. M/F 0.51654, 0.51635-0.51672). There was a male excess of 113,818 live births.There was a significant positive correlation between GDP% and M/F for Armenia, Azerbaijan and Uzbekistan. There was a significant negative correlation in Estonia.

CONCLUSION

Previous studies have shown that improving socioeconomic conditions increase M/F, and the converse has also been demonstrated. This is a potential influence in this geographical area since this region has relatively recently emerged from communist rule and experienced an overall economic upturn, but is only partially supported using GDP%. Another factor may be the selective termination of female pregnancies. The latitude gradient parallels that of neighbouring Europe but no theory has been put forward to convincingly explain this finding to date.

Sex ratios at birth in Scandinavia over the past sixty years

BACKGROUND

The gender ratio at birth (M/F: male births divided by total births) is expected to approximate 0.515. This has shown to be declining in industrialised countries and to display a latitude gradient in Europe, with more males born in southern climates.

METHODS

Annual national data for Scandinavian countries for male and female live births were obtained from the World Health Organisation and analysed with contingency tables.

RESULTS

This study analysed 18,250,193 live births. A significant decreasing trend in M/F was noted in all countries except Norway, and overall. There was no latitude gradient. M/F was less than 0.515 for almost all countries, with a resultant male deficit of 19,517 live births.

CONCLUSIONS

M/F is decreasing in Scandinavia and M/F overall is <0.515. The interaction of several poorly comprehended factors is likely.

Parasite stress predicts offspring sex ratio

In this study, I predict that the global variation of offspring sex ratio might be influenced in part by the level of parasite stress. From an energetic standpoint, higher gestational costs of producing a male offspring could decrease male births in a population with limited resources. This implies that, any factor that limits the parental resources could be expected to favor female offspring production. Human sex ratio at birth (SRB) is believed to be influenced by numerous socioeconomic, biological, and environmental factors. Here, I test a prediction that parasite stress, by virtue of its effects on the general health condition, may limit the parental investment ability and therefore could influence the SRB at the population level. The statistical analysis supports this prediction, and show that the level of parasite stress has a significant inverse relation with population SRB across the world. Further, this relation is many-folds stronger than the association of SRB with other factors, like; polygyny, fertility, latitude, and son-preference. Hence, I propose that condition affecting ability of parasites (but not adaptive significance) could be a likely causal basis for the striking variation of SRB across populations.

Photons and evolution: quantum mechanical processes modulate sexual differentiation

This paper will show that the fractional difference in the human gender ratio (GR) between the GR(at death) for those born in solar cycle peak years (maxima) and the GR(at death) in those born in solar cycle non-peak years (minima), e.g., 0.023, divided by Pi, yields a reasonable approximation of the quantum mechanical constant, alpha, or the fine structure constant (FSC) approximately 0.007297... or approximately 1/137. This finding is based on a sample of approximately 50 million cases using common, readily available demographic data, e.g., state of birth, birth date, death date, and gender. Physicists Nair, Geim et al. had found precisely the same fractional difference, 0.023, in the absorption of white light (sunlight) by a single-atom thick layer of graphene, a carbon skeleton resembling chicken wire fencing. This absorption fraction, when divided by Pi, yielded the FSC and was the first time this constant could "so directly be assessed practically by the naked eye". As the GR is a reflection of sexual differentiation, this paper reveals that a quantum mechanical process, as manifested by the FSC, is playing a role in the primordial process of replication, a necessary requirement of life. Successful replication is the primary engine driving evolution, which at a biochemical level, is a quantum mechanical process dependent upon photonic energy from the Sun. We propose that a quantum-mechanical, photon-driven chemical evolution preceded natural selection in biology and the mechanisms of mitosis and meiosis are manifestations of this chemical evolution in ancient seas over 3 billion years ago. Evolutionary processes became extant first in self-replicating molecules forced to adapt to high energy photons, mostly likely in the ultraviolet spectrum. These events led to evolution by natural selection as complex mixing of genetic material within species creating the variety needed to match changing environments reflecting the same process initiated at the dawn of life. Both evolutionary mechanisms coexist and are interactive. The periodic energy of solar maxima is likely modulating the human genome from maternal integument to an embryo in utero with non-local mechanisms intrinsic to quantum mechanics.

Humans at tropical latitudes produce more females

Skews in the human sex ratio at birth have captivated scientists for over a century. The accepted average human natal sex ratio is slightly male biased, at 106 males per 100 females or 51.5 per cent males. Studies conducted on a localized scale show that sex ratios deviate from this average in response to a staggering number of social, economical and physiological variables. However, these patterns often prove inconsistent when expanded to other human populations, perhaps because the nature of the influences themselves exhibit substantial cultural variation. Here, data collected from 202 countries over a decade show that latitude is a primary factor influencing the ratio of males and females produced at birth; countries at tropical latitudes produced significantly fewer boys (51.1% males) annually than those at temperate and subarctic latitudes (51.3%). This pattern remained strong despite enormous continental variation in lifestyle and socio-economic status, suggesting that latitudinal variables may act as overarching cues on which sex ratio variation in humans is based.

Effect of 1-month war in Lebanon on sex ratio

Our study showed no effect of 33-day war in Lebanon on sex ratio. More research is needed to explore other modifying factors for a better understanding of the complex effect of wars on sex ratio changes.

Peaks of solar cycles affect the gender ratio

In this study, we report that the gender ratio (GR) at death [where GR=(N(males)/N(males)+N(females))] of those born (and likely conceived) in solar cycle peaks (about a 3-year period occurring on average every approximately 11 years), is inversely related to mean male age at death; e.g., the higher the GR(at death) the lower the mean lifespan, while the GR(at death) of those born in non-peak years has no relation to mean male lifespan. Although changes in the GR are small and may be of little clinical significance, the GR is a sensitive indicator of environmental effects, and therefore is pertinent to epigenetics. This paper supports the hypothesis that solar radiation, probably in the ultraviolet spectrum, by some manner interacts with chromosomal DNA (genes) and produces the genetic variety that not only fosters adaptation, but also produces the diseases that reduce lifespan. This paper also proposes that sunlight is more effective in modifying genomes at the time of conception than later in gestation or infancy. Referring to the work of others, this study also reveals that geographic latitude also affects the GR, suggesting that the variation in light is probably as important as the intensity of light in modifying genomes. This study finds that men sustain more genetic variation, producing 28% more disease than women, as well as a 2% decrease in GR from birth to death, and a shorter life (in Maine) by 7 years.

Effect of the Lebanese civil war on sex ratio

Sex ratio is a subject of scientific interest but little is known about the factors that affect the sex ratio of humans. The aim of this study was to assess the effect of the Lebanese civil war on sex ratio. Data on all live births delivered at a large university hospital for the years 1977-2005 were used in this study. Study periods were defined as wartime (1977-1992) and post-war (1993-2005). The sex ratio in the study time period was calculated as the male proportion, i.e. males/males + females in live-born infants. Sex ratio during the war was compared with that of the post-war period. The sex ratio was similar in the war and post-war period (0.515 versus 0.513; OR = 1.007; 95% CI 0.98-1.04). The annual variation in the sex ratio during the study period did not show any significant change in any of the years. In conclusion, the Lebanese civil war did not cause a detectable change in sex ratio at birth. Factors that might have affected the sex ratio include the nature of the study population (civilians), the variable intensity of war in different periods, and the effect of stress and environmental toxins.

Effects of low-level radio-frequency (3kHz to 300GHz) energy on human cardiovascular, reproductive, immune, and other systems: A review of the recent literature

OBJECTIVES

Occupational or residential exposures to radio-frequency energy (RFE), including microwaves, have been alleged to result in health problems. A review of recent epidemiological studies and studies of humans as subjects in laboratory investigations would be useful.

METHODS

This paper is a narrative review of the recent medical and scientific literature (from mid-1998 through early 2006) dealing with possible effects of RFE on humans, relating to topics other than cancer, tumors, and central nervous system effects (areas covered in a previous review). Subject areas in this review include effects on cardiovascular, reproductive, and immune systems.

RESULTS

A large number of studies were related to exposures from cellular telephones. Although both positive and negative findings were reported in some studies, in a majority of instances no significant health effects were found. Most studies had some methodological limitations. Although some cardiovascular effects due to RFE were reported in epidemiological studies (e.g., lower 24-h heart rate, blunted circadian rhythm of heart rate), there were no major effects on a large number of cardiovascular parameters in laboratory studies of volunteers during exposure to cell-phone RFE. In population-based studies of a wide range of RFE frequencies, findings were equivocal for effects on birth defects, fertility, neuroblastoma in offspring, and reproductive hormones. Some changes in immunoglobulin levels and in peripheral blood lymphocytes were reported in different studies of radar and radio/television-transmission workers. Due to variations in results and difficulties in comparing presumably exposed subjects with controls, however, it is difficult to propose a unifying hypothesis of immune-system effects. Although subjective symptoms may be produced in some sensitive individuals exposed to RFE, there were no straightforward differences in such symptoms between exposed and control subjects in most epidemiological and laboratory studies. Consistent, strong associations were not found for RFE exposure and adverse health effects. The majority of changes relating to each of the diseases or conditions were small and not significant.

CONCLUSIONS

On the basis of previous reviews of older literature and the current review of recent literature, there is only weak evidence for a relationship between RFE and any endpoint studied (related to the topics above), thus providing at present no sufficient foundation for establishing RFE as a health hazard.

Altering systemic acid-base balance through nutrition failed to change secondary sex ratio

There is evidence that differences in either maternal blood pH or dietary mineral content can result in alterations in secondary sex ratio in mammals. Altering the proportions of certain dietary minerals is known to influence blood pH, offering a possible explanation for this effect of diet on secondary sex ratio. The present study was performed to investigate whether altering blood pH by manipulating the dietary cation-anion difference (DCAD) would alter secondary sex ratio. The DCAD is calculated (in mEq per 100 g dry matter) as the difference between metabolically strong cations (Na + K) and metabolically strong anions (Cl + S) in the diet. Three hundred female mice were randomly allocated to either a low or high DCAD ration for 3 weeks before coitus. Urine pH was monitored before beginning the experiment, as well as before and after the breeding period, as a proxy for blood pH. Mice on the low DCAD diet had a lower urine pH (mean (+/- s.d.) 6.0 +/- 0.1) than mice on the high DCAD diet (8.2 +/- 0.6), but DCAD did not affect the percentage of mice that became pregnant, the number of offspring per pregnant mouse or the sex ratio of the neonate group. These results suggest that blood pH alone does not alter sex ratio and that an altered systemic pH is not the reason for reported mineral-related variations in sex ratio.

Climatic variability and the population dynamics of historical hunter-gatherers: the case of Sami of Northern Finland

Our current knowledge on climate-mediated effects on human population dynamics is based on preindustrial agrarian societies where climate-induced crop failures had a major impact on fertility and mortality rates. However, because most of the human evolutionary history has been shaped by hunter-gatherer lifestyle relying on diverse plant and animal food sources, it is also important to understand how climate affected the population dynamics of hunter-gatherers. We thus studied whether climate, measured as a reconstructed annual mean temperature, had concurrent or delayed effects on the key components of population dynamics, annual births and deaths, in three historical (1722-1850) Sami populations of Northern Finland that depended mainly on fishing, hunting, and reindeer herding for their livelihood. We found only weak concurrent effects of mean temperature on annual births and deaths, although in general warm years correlated with increased birth and reduced mortality rates. Likewise, temperature-mediated delayed effects were mainly absent: in one population only, a warm previous year tended to reduce the number of births. By contrast, annual numbers of births and deaths were more closely associated, as indicated by negative correlations between births and deaths up to three previous years. To summarize, in contrast to historical agrarian societies, the population dynamics of historical Sami seemed to be only weakly associated with annual mean temperature, which may indicate that these populations, probably due to their dietary breadth, were rather unaffected by climatic variation.

Climatic factors and secondary sex ratio in dairy cows

The hypothesis for this study was that the prevailing climate around the time of conception was associated with changes in the secondary sex ratio (SSR) in grazing, seasonally bred dairy cattle. Calving date, parity, cow breed, and calf sex were obtained for 8,621 lactations (with single births only) from 1,897 cows between 1970 and 2003 (inclusive). Conception date was estimated by subtracting a gestation length of 282 d from the date at calving. Climatic factors, including maximum and minimum ambient temperature, relative humidity, rainfall, sunlight hours, and evaporation rate, were averaged across the week immediately prior to conception for all lactations. Sun radiation data were available after 1976. Generalized estimating equations, with cow included as a repeated effect, were used to determine the effect of climate around the time of conception on the logit of the probability of a male calf. Breed of cow, year of conception, and parity at conception did not affect the SSR. The odds of a male calf being born were 3.74 times greater when the immediately previous calf born was male. A male calf was more likely to be born following periods of elevated air temperature, greater evaporation, or both. A 1 degrees C increase in average maximum air temperature from the average (18.3 degrees C), during the week immediately prior to conception, was associated with a 1-percentage unit increase in the probability of a male calf being born (i.e., from 52 to 53%). A corresponding 1 degrees C increase in average minimum air temperature was reflected in a 0.5-percentage unit increase in the probability of a male calf being born. The probability of a male calf being born increased by 2.9 percentage units with each additional millimeter of evaporation per day. Results indicate that climatic factors associated with elevated temperatures and greater evaporation may influence the SSR in dairy cattle.

Pre-conception energy balance and secondary sex ratio--partial support for the Trivers-Willard hypothesis in dairy cows

According to the Trivers-Willard hypothesis, maternal condition at or around conception affects the secondary sex ratio in mammals. However, there are little or no data available on indicators of maternal condition in dairy cows on the sex of the resultant offspring. A total of 76,607 body condition score (BCS; scale of 1 to 5) records and 76,611 body weight (BW) records from 3,209 lactations across 1,172 cows were extracted from a research database collated from one research herd between 1986 and 2004, inclusive. Exclusion of multiple births and cows with no information before calving (e.g., nulliparous animals) resulted in 2,029 records with BCS and BW observations from the previous calving, and 2,002 and 1,872 lactations with BCS and BW observations at conception and midgestation, respectively. Change in BCS and BW between calving and conception and between conception and midgestation was calculated per lactation. Generalized estimating equations were used to model the logit of the probability of a male calf, in which cow was included as a repeated effect with a first-order autoregressive correlation structure assumed among records within cow. Of the BCS variables investigated, there was a linear relationship between the logit of the probability of a male calf and BCS change between calving and conception, the rate of BCS change over this period (BCS divided by days in milk), and BCS at the calving event immediately before conception. The birth of a bull calf was 1.85 times more likely in cows that lost no BCS from calving to conception compared with cows that lost one BCS unit from calving to conception. This increase in odds was equivalent to a 14% unit increase in the probability of a male calf (from 54 to 68%). The amount of BW lost between calving and conception and the rate of loss affected the sex of the resultant offspring. Less BW loss or greater BW gain between calving and conception was associated with greater likelihood of a male calf. Results suggested a positive effect of pre-conception BCS and BW change on secondary sex ratio, agreeing with the Trivers-Willard hypothesis that females in good physiological condition are more likely to produce male offspring.

Secular trends in sex ratios at birth in North America and Europe over the second half of the 20th century

CONTEXT

A previous study showed that significantly more boys were born in southern latitudes in Europe than in northern latitudes and the converse pattern was observed in North America.

OBJECTIVE

This study analyses secular trends in gender ratios for live births over the second half of the 20th century.

DESIGN, SETTING, PARTICIPANTS

Analysis was carried out from a World Health Organisation dataset comprising live births over the above period. This included 127034732 North American and 157947117 European live births.

MAIN OUTCOME MEASURES

Analysis of trends in gender ratios for countries in both continents.

RESULTS

The findings show a highly significant overall decline in male births in both Europe and North America (p<0.0001), particularly in Mexico (p<0.0001). Interestingly, in Europe, male births declined in North European countries (latitude>40 degrees, p<0.0001) while rising in Mediterranean countries (latitude congruent with 35-40 degrees, p<0.0001). These trends produced an overall European male live birth deficit 238693 and a North American deficit of 954714 (total male live birth deficit 1193407).

CONCLUSIONS

No reasonable explanation/s for the observed trends have been identified and the causes for these trends may well be multifactorial.

Hot male: can sex in humans be modified by temperature?

Sex determination in many animals has an environmental component, particularly through temperature. In this article, it is argued that some evidence may by seen for this in humans, and it is proposed that the influence of temperature on sex determination may be a reason for the placing of testicles outside the body cavity in most male mammals.

Environmental factors and the proportion of males at birth in Italy

A significant decline in the proportion of male births has been observed in recent decades in several western countries, and several researchers have raised the question of the possible role of environmental pollution in this trend. In the present analysis, the authors examined the effect of environmental factors (pollution from pesticides, urban pollution, and industrial pollution) on the sex ratio (proportion of males) of Italian singleton 1st births for the years 1989-1993, controlling for the age of the mother. The data show a slight increase in the sex ratio from north to south; however, no reduction in the proportion of males was seen in areas with higher pesticide consumption or intense industrial pollution. A small reduction in sex ratio was found in the major urban centers. The analysis was based on individual information on birth order and maternal age, as well as on ecological data on environmental pollution. No significant association was found between environmental pollution and the proportion of male births in Italy during the study period.

Infertility and environmental pollutants

While it has long been known that female fertility is impaired by oestrogen exposure, it is unclear whether environmental pollutants with weak oestrogenic effects are sufficiently potent and prevalent to have biological effects in humans. Male fertility, or sperm concentration at least, appears to have deteriorated, and there is substantial spatial variation at both national and global level, as well as a genetic component. Sperm morphology and motility are implicated too. There is good evidence for an increase in testicular cancer, and possibly in other conditions that certain spatial characteristics plus evidence on heritability suggest are linked to impaired spermatogenesis. A candidate agent would need to have started increasing in the early 20th century. Weak environmental oestrogens are not responsible. Candidates include agents affecting endogenous maternal oestrogen levels, environmental anti-androgens (although these cannot explain the epidemiological findings), and dioxin and related compounds. Genetic damage should be considered as a unifying hypothesis, possibly focused on the Y-chromosome.

Reproductive outcomes in the women of the Red River Valley of the north. I. The spouses of pesticide applicators: pregnancy loss, age at menarche, and exposures to pesticides

In the current study, there was a modest but significant increase in risk (1.6- to 2-fold) for miscarriages and/or fetal loss occurring throughout the year in the spouses of applicators who use fungicides. There is a surprisingly significant deficit in the number of male children born to the spouses of fungicide applicators. First-trimester miscarriages occur most frequently in the spring, during the time when herbicides are applied. Use of sulfonylurea (odds ratio OR = 2.1), imidizolinone (OR = 2.6) containing herbicides, and the herbicide combination Cheyenne (OR = 2.9) by male applicators was statistically associated with increased miscarriage risk in the spring. Limited survey data from women who are the spouses of applicators did not show major alterations of long-term endocrinologic status (menarche, menopause, endometriosis). With regard to personal pesticide exposures, only women who engaged in pesticide application where there is direct exposure to these products are at demonstrable risk (OR = 1.8) for miscarriage. It was hypothesized that the overall reproductive toxicity observed in this population is, for the greater part, a male-mediated event. Clarification of exposure events leading to reproductive toxicity through direct measurements of exposure in both men and women is needed to resolve this issue.