Seasonal variation in high density lipoprotein cholesterol

Effects of combined physical exercise on plasma lipid variables, paraoxonase 1 activity, and inflammation parameters in adults with obesity: a randomized clinical trial

OBJECTIVE

We aimed to investigate whether combined physical exercise may affect plasma lipid variables, paraoxonase 1 (PON1) activity, and inflammation parameters in adults with obesity.

METHODS

Thirty-six participants were recruited to complete the study protocol. The mean age was 37 ± 1 years, and the baseline body mass index was 33.0 ± 0.4 kg/m². Participants were allocated to the control group (CG) and the exercise group (EG). The EG performed three weekly sessions of combined physical exercise for 16 weeks. Plasma lipid variables, PON1 activity, and inflammatory profile were determined before and after intervention.

RESULTS

Total cholesterol levels decreased in both groups, without intergroup difference (time p = 0.001). Non-high-density lipoprotein cholesterol (HDL-C) levels decreased in both groups (time p = 0.001); however, they were lower in the EG than in the CG (p = 0.038). The EG had increased HDL-C levels, but the CG had decreased HDL-C levels (time*group p = 0.011). PON1 activity was reduced in both groups (time, p = 0.001). The Castelli risk Index I and II reduced in the EG and increased in the CG (time*group, p = 0.008 and p = 0.011, respectively). The inflammatory markers were not modified.

CONCLUSION

Adults with obesity may benefit from regular practice of combined physical exercise training in many metabolic aspects that are related to protection against the development of cardiovascular disease.

Data mining: traditional spring festival associated with hypercholesterolemia

BACKGROUND

Serum lipid concentrations are affected by long-term high-fat diets; thus, we hypothesize that lipid levels increase after the Spring Festival in China.

METHOD

In total, 20,192 individuals (male: n=10,108, female: n=10,084) were enrolled in this retrospective cross-sectional study based on clinical data from the Laboratory Information System (LIS) and Hospital Information System (HIS) in Peking Union Medical College Hospital from 2014 to 2018. Total cholesterol (TC), triglycerides (TGs), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were analyzed.

RESULTS

The serum TC [male vs. female: (4.71 ± 0.90 vs. 4.56 ± 0.85) mmol/L], TG [male vs. female: (1.71 ± 1.56 vs. 1.02 ± 0.68) mmol/L], and LDL-C [male vs. female: (3.01 ± 0.77 vs. 2.73 ± 0.74) mmol/L] levels were significantly higher in males than in females (P < 0.001); serum HDL-C [male vs. female: (1.18 ± 0.28 vs. 1.50 ± 0.34) mmol/L] was significantly lower in males (P < 0.001). In February, the TC, TG, and LDL-C levels were 8.4%, 16.3%, and 9.3% higher than the lowest levels recorded, respectively. The prevalence of dyslipidemia of the two weeks before the Spring festival was significantly lower than that of the first week after the Spring festival (43.6% (168/385) vs. 54.1% (126/233), P=0.007). Additionally, the prevalence of dyslipidemia was statistically higher in the first week after the Spring Festival than in May-January.

CONCLUSION

Higher TC, TG, and LDL-C in winter could be associated with high-fat diets during the Spring Festival. The Spring Festival was immediately followed by a higher lipid concentrations. Thus, we don't recommend lipid assessment or physical examination immediately after the holiday especially Spring festival.

Time series decomposition into dyslipidemia prevalence among urban Chinese population: secular and seasonal trends

BACKGROUND

Previous epidemiological studies have indicated the seasonal variability of serum lipid levels. However, little research has explicitly examined the separate secular and seasonal trends of dyslipidemia. The present study aimed to identify secular and seasonal trends for the prevalence of dyslipidemia and the 4 clinical classifications among the urban Chinese population by time series decomposition.

METHODS

A total of 306,335 participants with metabolic-related indicators from January 2011 to December 2017 were recruited based on routine health check-up systems. Multivariate direct standardization was used to eliminate uneven distributions of the age, sex, and BMI of participants over time. Seasonal and trend decomposition using LOESS (STL decomposition) was performed to break dyslipidemia prevalence down into trend component, seasonal component and remainder component.

RESULTS

A total of 21.52 % of participants were diagnosed with dyslipidemia, and significant differences in dyslipidemia and the 4 clinical classifications were observed by sex (P <0.001). The secular trends of dyslipidemia prevalence fluctuated in 2011-2017 with the lowest point in September 2016. The dyslipidemia prevalence from January to March and May to July was higher than the annual average (λ = 1.00, 1.16, 1.06, 1.01, 1.02, 1.03), with the highest point in February. Different seasonal trends were observed among the 4 clinical classifications. Compared to females, a higher point was observed among males in February, which was similar to participants aged < 55 years (vs. ≥ 55 years) and participants with a BMI ≤ 23.9 (vs. BMI > 23.9).

CONCLUSIONS

There were significant secular and seasonal features for dyslipidemia prevalence among the urban Chinese population. Different seasonal trends were found in the 4 clinical classifications of dyslipidemia. Precautionary measures should be implemented to control elevated dyslipidemia prevalence in specific seasons, especially in the winter and during traditional holidays.

Seasonal weight variation patterns in seven countries located in northern and southern hemispheres

The digital revolution of information and technology in late 20th century has led to emergence of devices that help people monitor their weight in a long-term manner. Investigation of population-level variations of body mass using smart connected weight scales enabled the health coaches acquire deeper insights about the models of people's behavior as a function of time. Typically, body mass varies when the seasons change. That is, during the warmer seasons people's body mass tend to decrease while in colder seasons it usually moves up. In this paper we study the seasonal variations of body mass in seven countries by utilization of linear regression. Deviation of monthly weight values from the starting point of astronomical years (beginning of spring) were modeled by fitting orthogonal polynomials in each country. The distinction of weight variations in southern and northern hemispheres were then investigated. The studied population involves 6429 anonymous weight scale users from:(1) Australia, (2) Brazil, (3) France, (4) Germany, (5) Great Britain, (6) Japan, and (7) United States of America. The results suggest that there are statistically significant differences between the models of weight variation in southern and northern hemispheres. In both northern and southern hemispheres the lowest weight values were observed in the summer. However, the highest weight values were noticed in the winter and in the spring for northern and southern hemispheres, respectively.

Analyzing Seasonal Variations in Suicide With Fourier Poisson Time-Series Regression: A Registry-Based Study From Norway, 1969-2007

Seasonal variation in the number of suicides has long been acknowledged. It has been suggested that this seasonality has declined in recent years, but studies have generally used statistical methods incapable of confirming this. We examined all suicides occurring in Norway during 1969-2007 (more than 20,000 suicides in total) to establish whether seasonality decreased over time. Fitting of additive Fourier Poisson time-series regression models allowed for formal testing of a possible linear decrease in seasonality, or a reduction at a specific point in time, while adjusting for a possible smooth nonlinear long-term change without having to categorize time into discrete yearly units. The models were compared using Akaike's Information Criterion and analysis of variance. A model with a seasonal pattern was significantly superior to a model without one. There was a reduction in seasonality during the period. Both the model assuming a linear decrease in seasonality and the model assuming a change at a specific point in time were both superior to a model assuming constant seasonality, thus confirming by formal statistical testing that the magnitude of the seasonality in suicides has diminished. The additive Fourier Poisson time-series regression model would also be useful for studying other temporal phenomena with seasonal components.

Association of cold ambient temperature and cardiovascular markers

Cardiovascular mortality has been shown to increase in the winter. However, it is unclear whether cold temperature affects indicators known as cardiovascular markers. We evaluated the association between ambient temperature and cardiovascular markers using data collected retrospectively from 55,567 adults who had visited a health check-up clinic between 1995 and 2008. Non-parametric smoothing regressions were fitted to determine the shapes of association between temperature and cardiovascular markers such as blood pressure, lipid profiles, platelet count, and high sensitivity C-reactive protein (hsCRP). Mixed effect model was used to investigate the significance of the relationship between temperature and cardiovascular markers. Decreased ambient temperature was associated with an increase in systolic and diastolic blood pressures, platelet count and serum low density lipoprotein-cholesterol concentration. In contrast, high density lipoprotein-cholesterol level declined with decreasing temperature. The hsCRP level increased with decreasing temperature in the minimum temperatures below 0°C, but revealed a reverse association above. Our study suggests that excess cardiovascular mortality in cold weather might be associated with temperature-related variations of cardiovascular markers.

Effects of aerobic and strength-based training on metabolic health indicators in older adults

BACKGROUND

The weakening of the cardiovascular system associated with aging could be countered by increasing levels of physical activity and functional fitness. However, inconsistent findings have been found, and the variety of characteristics of exercise used in previous studies may partly explain that inconsistent results.

OBJECTIVE

To investigate the training effect of sixteen weeks of moderate intensity, progressive aerobic and strength-based training on metabolic health of older women and men.

METHODS

Sixty three sedentary individuals (mean (SD) age 76 (8) years) were randomly assigned to control (n = 31) or exercising (n = 32) groups. The training group was separated to aerobic (n = 18) or strength-based (n = 14). Training took place three times a week. Subjects agreed not to change their diet or lifestyle over the experimental period.

RESULTS

Exercising group attained after treatment significant differences on body weight, waist circumference, body mass index, diastolic blood pressure, triglycerides, total cholesterol, HDL-cholesterol, LDL-cholesterol, total cholesterol/HDL-cholesterol relationship, high sensitivity C-reactive protein, and 6-minute walk distance. The control group only had significant differences on waist circumference.

CONCLUSION

The training programs produced significant benefits on metabolic health indicators of sedentary older women and men.

Seasonal changes in amount and patterns of physical activity in women

BACKGROUND

Environmental factors including seasonal changes are important to guide physical activity (PA) programs to achieve or sustain weight loss. The goal was to determine seasonal variability in the amount and patterns of free-living PA in women.

METHODS

PA was measured in 57 healthy women from metropolitan Nashville, TN, and surrounding counties (age: 20 to 54 years, body mass index: 17 to 48 kg/m2) using an accelerometer for 7 consecutive days during 3 seasons within 1 year. PA counts and energy expenditure (EE) were measured in a whole-room indirect calorimeter and used to model accelerometer output and to calculate daily EE and intensity of PA expressed as metabolic equivalents (METs).

RESULTS

PA was lower in winter than in summer (131+/-45 vs. 144+/-54x10(3) counts/d; P=.025) and in spring/fall (143+/-48x10(3) counts/d; P=.027). On weekends, PA was lower in winter than in summer by 22,652 counts/d (P=.008). In winter, women spent more time in sedentary activities than in summer (difference 35 min/d; P=.007) and less time in light activities (difference -29 min/d, P=.018) and moderate or vigorous activities (difference -6 min/d, P=.051).

CONCLUSIONS

Women living in the southeastern United States had lower PA levels in winter compared with summer and spring/fall, and the magnitude of this effect was greater on weekends than weekdays.

Seasonal variation in lipids in patients following acute coronary syndrome on fixed doses of Pravastatin (40 mg) or Atorvastatin (80 mg) (from the Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis In Myocardial Infarction 22 [PROVE IT-TIMI 22] Study)

Previous studies have shown seasonal variation in lipids. To understand whether this variation exists in patients with acute coronary syndromes receiving statins, we examined data from the PROVE IT-TIMI 22 Study. At baseline, no significant difference in low-density lipoprotein (LDL) cholesterol was observed when stratified by season. However, a statistically significant difference in high-density lipoprotein cholesterol between winter (37 mg/dl) and summer (39 mg/dl) was observed (p <0.001) at baseline. On treatment, median LDL cholesterol was 102 mg/dl in winter versus 96 mg/dl in summer (p <0.001) for the pravastatin group and 68 mg/dl in winter versus 62 mg/dl in summer (p <0.001) for the atorvastatin group. Median high-density lipoprotein cholesterol was 43 mg/dl in summer versus 41 mg/dl in winter in the pravastatin group and 42 mg/dl in summer versus 39 mg/dl in winter in the atorvastatin group (p <0.001). More patients achieved LDL cholesterol <100 mg/dl in summer at 56% versus 47% in winter in the pravastatin group (p <0.001) and 89% versus 87% in winter for the atorvastatin group (p = 0.11). Achievement of LDL cholesterol <70 mg/dl was also higher in summer than winter. In conclusion, this was the first evidence of seasonal variability in cholesterol in patients with acute coronary syndromes treated with statins. This variability affected achievement of National Cholesterol Education Program goals and may affect management decisions based on season of collection.

Effects of strength and endurance training on metabolic risk factors in healthy 40-65-year-old men

This study compared 21 weeks of combined high-intensity strength and endurance training with endurance or strength training only on metabolic risk factors in 40-65-year-old men. The healthy men (n=63) were randomized into endurance (E), strength (S), combined strength and endurance training (SE) and control (C) groups. S and E trained two times a week and SE 2+2 times a week. Systolic (SBP) and diastolic blood pressure decreased significantly both in E (-6+/-8 and -4+/-6 mmHg) and in S (-9+/-8 and -5+/-7 mmHg), but not in SE or C (P=0.003 for the difference in the changes of SBP between the groups). The changes in serum glucose and insulin during an oral glucose tolerance test did not differ between the groups. Only E decreased serum fasting insulin levels (-17+/-27%, P=0.013). Minor changes were observed in blood lipids and lipoproteins in all groups. Both endurance and strength training can modestly improve metabolic health even in relatively lean older men with normal glucose tolerance. Combined strength and endurance training did not produce complementary benefits on metabolic risk factors. Combined training is effective in improving body composition and cardiorespiratory and muscular fitness, however, which is likely to decrease the risk of future metabolic and cardiovascular disease.

Community-based study on summer-winter differences of component of metabolic syndrome in Kinmen, Taiwan

BACKGROUND

A community-based study was conducted to investigate summer-winter differences of component of metabolic syndrome in Kinmen, Taiwan.

METHODS

A total of 8251 residents aged 40 and over were enrolled in the mass survey in Kinmen. They were investigated while on summer (July and August) and winter vacation (January and February) during 2000-2003. Demographics, physical examination findings, lifestyle variables and biochemical data were collected.

RESULTS

After controlling for age, body mass index, diet, lifestyle and other risk factors for component of metabolic syndrome, there were independent and significant relationships between summer-winter difference and component of metabolic syndrome. Winter season was positively correlated with blood pressure, fasting plasma glucose level, high-density lipoprotein-cholesterol (HDL-C) and waist circumference, but was negatively associated with fasting triglycerides and metabolic syndrome.

CONCLUSIONS

Summer season is positively associated with hypertriglyceridemia, low HDL-C and metabolic syndrome. These findings imply that cross-sectional, experimental and cohort studies of component of metabolic syndrome or metabolic syndrome should take season into account as possible confounding effects.

Seasonal patterns in monthly hemoglobin A1c values

The purpose of this study was to investigate seasonal variations in population monthly hemoglobin A(1c) (A1c) values over 2 years (from October 1998 to September 2000) among US diabetic veterans. The study cohort included 285,705 veterans with 856,181 A1c tests. The authors calculated the monthly average A1c values for the overall population and for subpopulations defined by age, sex, race, insulin use, and climate regions. A1c values were higher in winter and lower in summer with a difference of 0.22. The proportion of A1c values greater than 9.0% followed a similar seasonal pattern that varied from 17.3% to 25.3%. Seasonal autoregressive models including trigonometric function terms were fit to the monthly average A1c values. There were significant seasonal effects; the seasonal variation was consistent across different subpopulations. Regions with colder winter temperatures had larger winter-summer contrasts than did those with warmer winter temperatures. The seasonal patterns followed trends similar to those of many physiologic markers, cardiovascular and other diabetes outcomes, and mortality. These findings have implications for health-care service research in quality-of-care assessment, epidemiologic studies investigating population trends and risk factors, and clinical trials or program evaluations of treatments or interventions.

Seasonality of coronary artery deaths in New South Wales, Australia

BACKGROUND

Complex temporal variations in coronary deaths, including diurnal, weekly, and seasonal trends, have been reported worldwide.

OBJECTIVE

To describe the magnitude of seasonal changes in coronary artery deaths in New South Wales, Australia.

DESIGN

Hospital morbidity data, mortality statistics, and meteorological data were modelled using time series techniques to determine seasonality of coronary deaths. Data were also analysed to determine whether there was an increase in deaths before or after the Christmas and New Year holidays.

RESULTS

A clear seasonality of coronary deaths was shown, with a peak in July. A mean of 2.8 excess coronary deaths per 100 deaths was estimated to occur from June to August each year, with a mean annual excess of 224 winter deaths a year. Mortality data did not show an increase in coronary death ratios before (p = 0.626) or after (p = 0.813) the Christmas and New Year holidays in December.

CONCLUSIONS

There is a higher incidence of coronary deaths in winter, which may reflect winter respiratory infections, the direct effect of cold, seasonal changes in lipid concentration, and other factors associated with winter. Hospitals should have contingency plans during the winter months to manage larger numbers of cardiac admissions.

Effects of preventive group education on the resistance of LDL against oxidation and risk factors for coronary heart disease in bypass surgery patients

BACKGROUND

Comprehensive preventive education for heart patients is effective in reducing cardiac events. However, very demanding counselling protocols cannot easily be implemented as an integral part of clinical practice in hospitals.

AIM

To evaluate whether recurrent preventive group education for coronary artery bypass grafting patients affects the resistance of LDL against oxidation and the classical risk factors for coronary heart disease.

METHODS

A prospective, controlled study with one-year follow-up was carried out in Southern Finland. Coronary artery bypass patients were allocated late (> or = 18 months) after the operation in the intervention and control groups.

RESULTS

Seventy two patients (65 men and 7 women) completed the study. Twelve-hour group education on healthy life-style had a significant (25%, P = 0.01) but transient positive effect on the resistance of LDL against oxidation. There was a trend towards increased physical activity in the intervention group. The impact of education on patients' weight was also more consistent (1.2 kg at 12 months, P < 0.05), whereas long-term effects on fibrinogen and serum lipids were small.

CONCLUSIONS

Repeated group education applied as an economically feasible part of specialist care had only small positive effects on patients' risk factors. There was a significant, but transient, increase in the resistance of LDL against oxidation. However, effective lipid lowering drug treatment is indicated for most coronary artery bypass patients rather than repeated health education alone.

Seasonal variation of some metabolic and haemostatic risk factors in subjects with and without coronary artery disease

Acute myocardial infarction (AMI) is more frequent in winter months than in summer months. The aetiologic mechanisms underlying this seasonal pattern are poorly understood. We investigate whether seasonal variation of metabolic and haemostatic coronary risk factors exists, and whether this variation is more pronounced in subjects with coronary artery disease (CAD). In 82 subjects (47 free of clinical signs of CAD and in 35 survivors of AMI), measurements of body mass index (BMI), lipoproteins, glucose, insulin, plasminogen activator inhibitor-1, tissue-type plasminogen activator (t-PA), euglobulin clot lysis time, fibrinogen, and platelet count were performed twice in the cold months (December and March) and twice in the warm months (June and September). Significantly higher BMI (26.8 versus 26.2 kg/m2, P < 0.01), glucose (5.5 versus 5.1 mmol/l, P < 0.01), total cholesterol (5.61 versus 5.32 mmol/l, P < 0.05), low-density lipoprotein cholesterol (3.63 versus 3.34 mmol/l, P < 0.05), triglycerides (1.79 versus 1.61 mmol/l, P < 0.01), Lp(a) (270.7 versus 237.5 mg/l, P < 0.01), fibrinogen level (3.50 versus 2.95 g/l, P < 0.00001), platelet count (212 x 10(9) versus 173 x 10(9)/l, P < 0.01) and significantly lower high-density lipoprotein cholesterol level (1.22 versus 1.28 mmol/l, P < 0.05) were observed in the cold months compared with the warm months. Significant seasonal variation of t-PA activity (1.19 versus 0.87 IU/ml, P = 0.015) and t-PA antigen (8.5 versus 7.3 ng/ml, P = 0.05) was demonstrated only in subjects with CAD. Clustering of peak values of several metabolic and haemostatic coronary risk factors was observed in winter months. This variation might be of aetiopathogenetic importance for the seasonal pattern of acute myocardial infarction.

Influence of dietary intake and physical activity on annual rhythm of human blood cholesterol concentrations

Seasonal variation in the plasma total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C) have been repeatedly reported, with contradictory results regarding the pattern of seasonal variation of these parameters. Furthermore, it is still not well established whether the variation is due to changes in the nutrition or changes in physical activity depending on the season. The aim of this study was therefore to determine plasma TC and HDL-C in different groups of healthy participants: 19 vegetarians with a constant diet independent of the season, 14 athletes with almost constant physical activity over the year, and 114 controls in the age groups 20-26 years (mean age 24 + 1.5 years) and 40-48 years (mean age 44.3 + 2.1 years). Over 2 years, blood samples were collected every 2-3 months and were analyzed for plasma TC and HDL-C. At all visits, body mass index (BMI) and waist-to-hip ratio (WHR) were calculated, and nutrition and physical activity profiles were obtained. The seasonal model was calculated using object-oriented software for the analysis of longitudinal data in S (OSWALD); multiple regression analysis was used to determine the influence of age, gender, diet, and physical activity on seasonal changes of the lipid parameters. In all groups, we found an annual rhythm of the plasma TC and HDL-C concentrations, which can be mathematically described by a sine curve with a maximum in winter and a minimum in summer. This rhythm was independent of the age, gender, BMI, diet, or physical activity. The observed seasonal differences between the maximum and the minimum were about 5%-10% for TC and about 5%-8% for HDL-C concentration. These differences were greater than the determined circadian (TC 3.5%, HDL-C 4%) and day-to-day changes for TC and HDL-C (coefficient of variation <5% for both). In conclusion, annual rhythm of TC and HDL-C is not primarily induced by seasonal differences in dietary intake or physical activity. Therefore, the annual rhythm in cholesterol levels is most likely determined by endogenous factors or factors directly related to seasonal changes in the environment.

Seasonal variation in household, occupational, and leisure time physical activity: longitudinal analyses from the seasonal variation of blood cholesterol study

The authors examined seasonal variation in physical activity in longitudinal analyses of 580 healthy adults from Worcester, Massachusetts (the Seasonal Variation of Blood Cholesterol Study, 1994-1998). Three 24-hour physical activity recalls administered five times during 12 months of follow-up were used to estimate household, occupational, leisure time, and total physical activity levels in metabolic equivalent (MET)-hours/day. Trigonometric models were used to estimate the peak-to-trough amplitude and phase of the peaks in activity during the year. Total activity increased by 1.4 MET-hours/day (121 kcal/day) in men and 1.0 MET-hours/day (70 kcal/day) in women during the summer in comparison with winter. Moderate intensity nonoccupational activity increased by 2.0-2.4 MET-hours/day in the summer. During the summer, objectively measured mean physical activity increased by 51 minutes/day (95% confidence interval: 20, 82) in men and by 16 minutes/day (95% confidence interval: -12, 45) in women. The authors observed complex patterns of seasonal change that varied in amplitude and phase by type and intensity of activity and by subject characteristics (i.e., age, obesity, and exercise). These findings have important implications for clinical research studies examining the health effects of physical activity and for health promotion efforts designed to increase population levels of physical activity.

Chlamydia pneumoniae antibodies are associated with an atherogenic lipid profile

OBJECTIVE

To determine, within a representative population group of men and women, whether alteration of the lipid profile might underlie the reported association between Chlamydia pneumoniae and ischaemic heart disease.

DESIGN AND SETTING

Cross sectional survey in an area with a high incidence of ischaemic heart disease.

SUBJECTS

400 randomly selected participants in the World Health Organisation MONICA project's third population survey in Northern Ireland.

MAIN OUTCOME MEASURES

Stored sera were examined by microimmunofluorescence for IgG antibodies to C pneumoniae at a dilution of 1 in 64. Mean total and high density lipoprotein (HDL) cholesterol were compared between seropositive and seronegative individuals with adjustment for age, measures of socioeconomic status, smoking habit, alcohol consumption, body mass index, and the season during which blood had been taken.

RESULTS

In seropositive men, adjusted mean serum total cholesterol and HDL cholesterol were 0.5 mmol/l (9.2%) higher and 0.11 mmol/l (9.3%) lower, respectively, than in seronegative men. Differences in women did not achieve statistical significance, but both total cholesterol and HDL cholesterol were higher (3.6% and 5.8%, respectively) in seropositive than in seronegative individuals.

CONCLUSIONS

There is serological evidence that C pneumoniae infection is associated with an atherogenic lipid profile in men. Altered lipid levels may underlie the association between C pneumoniae and ischaemic heart disease.

Seasonal variation in parameters related to coronary heart disease risk in young men

Seasonal variation in the plasma lipids and lipoproteins is reported in the literature. Whether this variation is the result of changes in diet or other factors has not been adequately addressed. We investigated the effects of a controlled diet on the seasonal variation in the levels of plasma lipids and apolipoproteins and also on the excretion of urine metabolites of TXA2 and PGI2 in healthy males. Two well-controlled diet studies were conducted to evaluate effects of dietary fatty acids on plasma lipids (Studies 1 and 2; n = 33) and eicosanoid excretion (Study 2 only; n = 15). Participants consumed whole-food test diets in a randomized, four-period crossover design during each 26-day experimental period. A non-intervention control group also participated in each study (Study 1, n = 12; Study 2, n = 11). Blood was collected monthly and analyzed for plasma lipids and apolipoproteins A-1 (Apo A-1) and B100 (Apo B). Twenty-four hour urine samples were collected monthly only in Study 2 and analyzed for TXB2 and 6-keto-PGF1 alpha by RIA. Seasonal fluctuations were observed in all subjects in plasma Apo A-1 (zenith = July, with 95% CI June-July; P < 0.05) and Apo B (zenith = October, 95% CI September-November, P < 0.05). Although there was no significant variation in plasma cholesterol levels, the increase in Apo B is consistent with an increase in LDL particle number during the fall/winter. Additionally, excretion of both eicosanoid metabolites and the ratio of 6-keto-PGF1 alpha/TXB2 was markedly elevated in July (95% CI June-July, P < 0.001). Three seasonal fluctuations were observed both in participants who consumed a highly-controlled experimental diet and in the non-intervention controls. Thus, these results suggest a diet-independent seasonal variation in parameters thought to be involved in coronary heart disease risk status. An understanding of these variations is important not oly for clinical evaluation and metabolic study design issues, but more importantly, to clarify their clinical significance with the seasonal incidence of CHD events.