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!