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Vitamin D is essential to the modern indoor lifestyle
How much vitamin D do we need?
Children should be taking at least 400
to 1,000 international units of vitamin D
as a supplement every day, and adults
should take 1,500 to 2,000 IU.
Have there been clinical
trials showing the utility
of vitamin D?
Absolutely. For instance,
a trial of postmenopausal
women showed that tak-
ing vitamin D over four
years reduced their risk of
cancer by 60 percent.
What about pregnant or breast-feeding
We tested pregnant women who were
taking a prenatal vitamin containing 400 IU of vitamin D each day
and drinking two glasses of fortified
milk, and found that 76 percent of
them — and 81 percent of their newborns — were still vitamin D deficient
at the time of giving birth. We also estimate that most breast-feeding women
are vitamin D deficient, and they pass
along deficient milk to their infants.
Vitamin D deficiency has been linked to
increased risks of infectious diseases,
cancer, autoimmune diseases, heart
disease, cognitive decline, Parkinson’s
disease, asthma, mood disorders and
even diabetes. Is there biological evi-dence to show how vitamin D could
influence so many conditions?
Sure. For example, we know that
immune cells called macrophages
activate vitamin D, which causes cells
But don’t dermatologists counsel
people to limit their sun exposure?
Moderation in all things. Humans
evolved in sunlight. Our hunter-gatherer forebears were making thousands of units of vitamin D every day,
To what extent does the medical
community agree with you on vitamin D?
I recently gave a talk in Toronto to
internal medicine doctors and asked
how many of them were “believers,”
like it was a religious revival. And
90 percent raised their hands. The
test for vitamin D levels is now the
most ordered assay by doctors in the
United States. s