Vitamin D and Health in the 21st Century: Federal Initiatives to Advance Research

Predicting potential to benefit from an iron intervention: a randomized controlled trial of double-fortified salt in female Indian tea pluckers

OBJECTIVE

The present study examines characteristics of those who benefited from a dietary Fe intervention comprised of salt double-fortified with iodine and Fe (DFS).

DESIGN

Data from a randomized controlled trial were analysed to identify predictors of improved Fe status and resolution of Fe deficiency (serum ferritin (sFt) < 12 μg/l) and low body Fe (body Fe (BI) < 0·0 mg/kg) using non-parametric estimations and binomial regression models.

SETTING

A tea estate in West Bengal, India.

PARTICIPANTS

Female tea pluckers, aged 18-55 years.

RESULTS

Consuming DFS significantly (P = 0·01) predicted resolution of Fe deficiency (relative risk (RR) = 2·31) and of low BI (RR = 2·78) compared with consuming iodized salt. Baseline sFt (β = -0·32 (se 0·03), P < 0·001) and treatment group (β = 0·13 (se 0·03), P < 0·001) significantly predicted change in sFt. The interaction of baseline BI with treatment group (β = -0·11 (se 0·06), P = 0·08) predicted the change in BI. DFS did not significantly predict change in Hb and marginally predicted resolution of anaemia (Hb < 120 g/l).

CONCLUSIONS

Baseline Fe status, as assessed by sFt and BI, and consumption of DFS predict change in Fe status and resolution of Fe deficiency and low BI. Anaemia prevalence and Hb level, although simple and inexpensive to measure, may not be adequate to predict resolution of Fe deficiency in response to an intervention of DFS in similar populations with high prevalence of Fe deficiency and multiple nutritional causes of anaemia. These findings will guide appropriate targeting of future interventions.

Assessing vitamin status in large population surveys by measuring biomarkers and dietary intake - two case studies: folate and vitamin D

The National Health and Nutrition Examination Survey (NHANES) provides the most comprehensive assessment of the health and nutrition status of the US population. Up-to-date reference intervals on biomarkers and dietary intake inform the scientific and public health policy communities on current status and trends over time.

The main purpose of dietary assessment methods such as the food-frequency questionnaire, food record (or diary), and 24-hr dietary recall is to estimate intake of nutrients and, together with supplement usage information, describe total intake of various foods or nutrients. As with all self-reporting methods, these tools are challenging to use and interpret. Yet, they are needed to establish dietary reference intake recommendations and to evaluate what proportion of the population meets these recommendations. While biomarkers are generally expensive and, to some degree, invasive, there is no question as to their ability to assess nutrition status. In some cases biomarkers can also be used to assess intake or function, although rarely can one biomarker fulfill all these purposes. For example, serum folate is a good indicator of folate intake, red blood cell (RBC) folate is a good status indicator, and plasma total homocysteine is a good functional indicator of one-carbon metabolism.

Using folate and vitamin D – two vitamins that are currently hotly debated in the public health arena – as two case studies, we discuss the complexities of using biomarkers and total intake information to assess nutrition status. These two examples also show how biomarkers and intake provide different information and how both are needed to evaluate and set public health policy. We also provide guidance on general requirements for using nutrition biomarkers and food and supplement intake information in longitudinal, population-based surveys.

[Low vitamin D levels among patients at Semmelweis University: retrospective analysis during a one-year period]

Even in developed countries the prevalence of subjects with suboptimal vitamin D levels is high. The aim of this retrospective data analysis was to evaluate the prevalence of severe and moderate vitamin D deficiencies (defined as vitamin D levels<15 ng/ml and 15-30 ng/ml, respectively) among patients evaluated at Semmelweis University during a period between April, 2009 and March, 2010.

METHODS AND RESULTS

The average vitamin D level of 5808 subjects (3936 women and 1872 men) was 25.5 ± 10.9 ng/ml. The prevalence of moderate and severe vitamin D deficiency in whole population was 72% and 12%, respectively. Higher than normal vitamin D levels were measured in 0.8% of subjects. Female gender, older age and winter season were independent risk factors for vitamin D deficiency. Vitamin D levels were measured repeatedly in 1307 subjects. Interestingly, vitamin D levels measured later were lower compared to those measured at the first time (27.07±13.2 vs. 25.9±9.11 ng/ml, p<0.001). The prevalence of severe and moderate vitamin D deficiency was 8.1 and 71.5 per cent when vitamin D levels were measured at the second time. Of the 110 patients with severe vitamin D deficiency measured repeatedly only 11 patients (10%) presented with normal vitamin D levels at the second time.

CONCLUSIONS

These data indicate that severe and moderate vitamin D deficiencies are common in patients evaluated at Semmelweis University. Repeated measurements of vitamin D levels raise the notion that the efficacy of supplementation used for correction of vitamin D levels is not optimal.

[Skeletal and extra-skeletal consequences of vitamin D deficiency]

Vitamin D is obtained from cutaneous production when 7-dehydrocholesterol is converted to vitamin D(3) (cholecalciferol) by ultraviolet B radiation or by oral intake of vitamin D. Rickets appeared to have been conquered with vitamin D intake, and many health care professionals thought the major health problems resulting from vitamin D deficiency had been resolved. However, rickets can be considered the tip of the vitamin D deficiency iceberg. In fact, vitamin D deficiency remains common in children and adults. An individual's vitamin D status is best evaluated by measuring the circulating 25-hydroxyvitamin D (25(OH)D3) concentration. There is increasing agreement that the optimal circulating 25(OH)D3 level should be approximately 30 ng/mL or above. Using this definition, it has been estimated that approximately three-quarters of all adults have low levels. In utero and during childhood, vitamin D deficiency can cause growth retardation and skeletal deformities and may increase the risk of hip fracture later in life. Vitamin D deficiency in adults can exacerbate osteopenia and osteoporosis, cause osteomalacia and muscle weakness, and increase the risk of fracture. More recently, associations between low vitamin D status and increased risk for various non-skeletal morbidities have been recognized; whether all of these associations are causally related to low vitamin D status remains to be determined. The discovery that most tissues and cells in the body have vitamin D receptors and that several possess the enzymatic machinery to convert the 25-hydroxyvitamin D3, to the active form, 1,25-dihydroxyvitamin D3, has provided new insights into the function of this vitamin. Of great interest is its role in decreasing the risk of many chronic illnesses, including common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease. In this review I consider the nature of vitamin D deficiency, discuss its role in skeletal and non-skeletal health, and suggest strategies for prevention and treatment.

Inverse association between dietary vitamin D and risk of cutaneous melanoma in a northern Italy population

The possibility of an inverse association between vitamin D and risk of cancer and, in particular, of cutaneous malignant melanoma has been suggested, but results of epidemiologic studies are still conflicting. We examined the relation between dietary vitamin D intake and melanoma risk through a population-based case-control study (380 cases, 719 controls) in a northern region of Italy, a country with an average vitamin D intake lower than that in northern Europe or the United States. We assessed average daily intake of vitamin D from foodstuffs using the European Prospective Investigation into Cancer and Nutrition (EPIC) semiquantitative food frequency questionnaire. In this population, levels of vitamin D intake were considerably lower than those observed in recent U.S. studies. We found an inverse relation between dietary vitamin D and melanoma risk in the sample as a whole, in both crude and adjusted analyses. In sex- and age-specific analyses, this association appeared to be stronger among males and among older subjects. These findings suggest that, at the relatively low levels of intake observed in this sample, an inverse relation between dietary vitamin D and risk of cutaneous malignant melanoma may exist.

Does vitamin d deficiency cause hypertension? Current evidence from clinical studies and potential mechanisms

Vitamin D deficiency is widely prevalent across all ages, races, geographical regions, and socioeconomic strata. In addition to its important role in skeletal development and calcium homeostasis, several recent studies suggest its association with diabetes, hypertension, cardiovascular disease, certain types of malignancy, and immunologic dysfunction. Here, we review the current evidence regarding an association between vitamin D deficiency and hypertension in clinical and epidemiological studies. We also look into plausible biological explanations for such an association with the renin-angiotensin-aldosterone system and insulin resistance playing potential roles. Taken together, it appears that more studies in more homogeneous study populations are needed before a firm conclusion can be reached as to whether vitamin D deficiency causes or aggravates hypertension and whether vitamin D supplementation is safe and exerts cardioprotective effects. The potential problems with bias and confounding factors present in previous epidemiological studies may be overcome or minimized by well designed randomized controlled trials in the future.