ChemMatters | DECEMBER 2017/JANUAR Y 2018 5
ITAMINS SERVE MANY DIFFERENT
functions in our bodies, such as mak-
ing our bones strong and helping our
immune system fight infections. Most of our
daily requirements for these vitamins can
come from a healthy, natural diet.
But one notable exception is vitamin D,
which is naturally present in only a few foods.
Fortunately, it is the one type of vitamin our
body can produce on its own. That’s the good
news. The bad news is that we only produce
vitamin D when our skin is exposed to ultra-
violet (UV) light from the sun, something that
can increase our risk of skin cancer.
This creates a dilemma; how do we get
enough vitamin D when it is rare in most foods
and exposure to too much sun is harmful?
What is vitamin D, and
how do you get it?
Vitamin D produced by your body is derived
from cholesterol. Similar to vitamin A, vitamin
D exists in different chemical forms—D2 and
D3 (Fig. 1).
Your skin contains a compound called
7-dehydrocholesterol. When exposed to UVB
radiation, a specific type of UV rays from the
sun, 7-dehydrocholesterol spontaneously
converts into vitamin D3. Humans cannot
make vitamin D2.
Both forms of vitamin D can be obtained
from food. Very few foods in nature contain
vitamin D3. The flesh of fatty fish, such as
salmon, tuna, and mackerel, and fish liver
oils, are among the best sources. Small
amounts of vitamin D3 are found in beef liver,
cheese, and egg yolks.
Chemically, the D3 made in your skin and
the D3 from your diet are the same. A slightly
different form, called ergocalciferol or vitamin D2, comes from vegetables, such as
mushrooms and alfalfa. But since liver and
alfalfa are not popular food choices, where
does that leave us in getting enough
vitamin D to stay healthy?
Fortified foods to the rescue
Fortified foods have extra vitamins added
to them during production. For example, the
milk you buy at the supermarket is vitamin D
fortified. Also, many breakfast cereals, pastas,
milk substitutes, yogurts, as well as some
cheeses, juices, and margarine spreads are
fortified with vitamin D. One serving of each
food can provide between 10% and 25% of
the necessary amount to keep your body in a
healthy range of vitamin D consumption. Most
of us get our vitamin D from these fortified
Vitamin D fortification of foods is regulated
in the United States by the Food and Drug
Administration (FDA). While most of this fortification is done voluntarily by food producers, the FDA mandates that infant formula is
fortified due to the importance of vitamin D in
In addition, more than half of the adult
population takes some form of supplement
such as multivitamin pills. There is considerable debate among health experts about the
medical benefits of vitamin supplements and
whether they are necessary.
Your bones need vitamin D
Getting insufficient vitamin D can have serious health effects. Low vitamin D can result in
Figure 1. Humans can not synthesize vitamin D2. But UVB rays from sun exposure convert
7-dehydrocholesterol in the body to vitamin D3.
By David Warmflash
Vitamin D2 7-dehydrocholesterol Vitamin D3