Saturday, January 25, 2014

The Nutrition Debate #179: Vitamin D Supplementation

Supplementing with Vitamin D has become all the rage in recent years, but “Low concentrations of 25-hydroxyvitamin D (23[OH]D) are most likely an effect of health disorders and not a cause of illness,” according to a piece by Nancy A Melville here in Medscape Medical News.  Melville’s article on a “comprehensive review of observational studies and randomized clinical trials of vitamin-D status and health outcomes” was published online in Lancet Diabetes & Endocrinology. A previous large-cohort study had shown “strong associations” of low Vitamin D Concentrations (<30nmol/L) with all-cause, cardiovascular, cancer and respiratory disease mortality.

Vitamin D is an odd bird sort of “vitamin.” It is not, strictly speaking, an essential vitamin because, according to Wikipedia, it can be “synthesized in the skin, from cholesterol, when sun exposure is adequate.”However, people who live further from the equator get less exposure to the sun’s rays in winter. And people who work indoors get less exposure. And out of concerns for skin cancer, many people block sun exposure with lotions. In addition, the elderly population (mainly women), and others with limited mobility, have less opportunity to get vitamin-D by natural means.

So, “like other compounds called vitamins, in the developed world, vitamin-D is added to staple foods, such as milk, to avoid disease due to deficiency,” according to Wikipedia. The enthusiasm for Vitamin-D supplementation has been fueled by its “relatively low toxicity, the glimmer of positivity from some trials, and the large body of evidence from prospective observational studies,” according to the Medscape piece. In addition, the vitamin-D supplement industry, the manufacturers of vitamin-D testing products, and the artificial UV tanning industry have all helped fuel the enthusiasm.

“The new analysis,” according to Medscape, “showed moderate to strong associations between lower concentrations of 25(OH)D and higher risk of conditions ranging from cardiovascular disease to infectious disease, glucose metabolism disorders, and mood disorders.” The researchers “found no effect on disease occurrence as a result of supplementation.”“The discrepancy between observational and interventional studies suggests that low 25(OH)D is a marker of ill health.” Quoting the Medscape piece, “In the interventional studies, participants had a baseline mean 25(OH)D concentration of less than 50nmol/L. Supplementation with 50µg/day of vitamin D resulted in no significant improvement in health status.” 50µg/day = 2000 iu.

This carte blanche Medscape excerpt addresses the effect of vitamin-D supplementation’s on diabetes and cancer.

“As part of their review, the authors also conducted a meta-analysis of 16 trials that focused on the effects of vitamin-D supplementation on HbA1c, the standard measure of long-term blood glucose control in diabetes. Although the observational studies showed an association between type 2 diabetes and low vitamin-D levels, supplementation with the vitamin had no effect on reducing HbA1c.

The data also showed that high 25(OH)D concentrations were associated with a protective effect on colorectal cancer, but not other cancers. However, 2 large intervention trials showed no reduced risk of any cancers, including colorectal, with vitamin-D supplementation.

One exception was seen in the elderly population (mainly women), who showed a slight reduction in all-cause mortality if they received vitamin-D supplementation of 20 µg/day (= 800 iu). However, the authors say that the improvement could be related to vitamin-D deficits caused not directly by the illness itself but by lifestyle changes resulting from the illness, such as a lack of mobility, restrictions on exposure to sunlight, or dietary modifications related to treatment.

‘In elderly people, restoration of vitamin-D deficits due to aging and lifestyle changes induced by ill health could explain why low-dose supplementation leads to slight gains in survival,’ they suggest.”

Ms Melville writes, “The authors speculate that a key mechanism that causes lower 25(OH) D concentrations in people with illness is disease-related inflammation.” “They add that ongoing trials will provide more information, but in the meantime they advise against vitamin-D supplementation. In addition, Ms Melville quotes Dr. Autier as saying, “…supplementation, if an individual’s vitamin-D concentration falls below a ‘sufficiency’ threshold of 75nmol/L, (is) an ill-advised practice.”

He added, “The wealth of evidence from randomized trials shows that this medical behavior is not grounded, and taking vitamin-D supplements will make no difference in health status.” “It would be wiser to seek reasons underlying the low vitamin-D level, such as inflammatory processes, or undiagnosed cardiovascular diseases, and fix them.
This was a serious review and an excellent job by Medscape of reporting on it. If you supplement with Vitamin D, you should at the very least read this Medscape piece for a fuller and easy-to-understand summary and analysis of the paper. And get some sun!

1 comment:

  1. I want to thank you for the superb post!! I surely liked every bit of it. I?ve bookmarked your internet site so I can take a appear at the latest articles you post later on. Best Urology hospital in jaipur