Vitamin D is a fat-soluble prohormone (a hormone that is converted by
the body to the active form). It helps the body absorb calcium and
regulate the levels of the minerals calcium and phosphorus in the
bloodstream. Vitamin D is naturally found in oily fish, shellfish, eggs,
beef liver, fish liver oils, and mushrooms. Certain foods such as milk
and cereals are also fortified with artificial vitamin D.
Vitamin D is also produced by the skin of humans and most other animals
by a chemical reaction between a form of cholesterol and ultraviolet
(UV) light, from the sun or sun-lamps. The good news—a little exposure
is enough. If you were to go out into the summer sun in your bathing
suit for a few minutes, you will have produced much more vitamin D than
what the government says you need. The skin also prevents your body from
producing too much vitamin D, preventing certain toxic effects. Melanin,
the dark pigment of the skin, UV blocking sunscreens, age and the weaker
sunlight of northern regions decrease the amount of vitamin D produced
by sunlight. Whether through diet or exposure to the sun, what you start
out with is cholecalciferol, a kind of pre-vitamin D. Cholecalciferol is
converted by the liver and the kidneys to the active form of vitamin D.
Since vitamin D helps the body to absorb calcium, it is important to
bone health. It may also help to increase muscle strength. Many studies
have shown that vitamin D deficiency has been associated with fractures
from falls in older adults. A decreased risk of colon cancer in people
with higher vitamin D levels was reported in another study. Some
researchers have concluded that vitamin D has a protective effect on the
heart and suppresses inflammation. Vitamin D has a role in regulating
the immune system. It is thought that, because of its strong
anti-inflammatory effect and immune system support, vitamin D
deficiencies might contribute to autoimmune diseases such as multiple
sclerosis (MS), type I diabetes and rheumatoid arthritis. There are
other, less conclusive studies that hint that vitamin D may help prevent
type 2 diabetes and depression. The sunshine vitamin has much potential,
but more research needs to be done in some areas.
Vitamin D deficiency
It has been estimated that 1 billion people, worldwide, have vitamin D
deficiency. Vitamin D deficiency most commonly causes osteomalacia, a
softening of the bones. A more severe form of osteomalacia in children
is known as rickets. Some people suffer from muscle weakness. For most
people, the symptoms of vitamin D deficiency are so subtle as to not be
The following are reasons that people become vitamin D deficient:
Diet: If you are a strict vegetarian,
or if you avoid dairy products, you may not consume
enough vitamin D in your diet.
Shun the sun? If you don’t get much
exposure to sunlight, such as living in a northern
climate, wearing robes that cover almost your entire
body (such as for religious reasons), or having an
occupation that keeps you out of the sun, your body does
not manufacture enough of its own vitamin D
Dark Skin: Melanin, the pigment that
colors the skin, inhibits the production of vitamin D.
Older adults with dark skin are particularly
Kidney (renal) problems: As you age,
your kidneys are less able to convert vitamin D to its
Digestion: Some conditions such as
Crohn’s disease, cystic fibrosis and celiac disease
inhibit the digestive tract from absorbing vitamin D.
Obesity: Fat cells absorb vitamin D
from the blood. Obese people are more commonly vitamin D
Testing to determine vitamin D deficiency
The best test to determine vitamin D deficiency is the assay for 25,
hydroxyvitamin D. Main Line Health Laboratories performs this vitamin D
test at Lankenau Medical Center in Wynnewood, PA. Total vitamin D from
its two major sources is measured: vitamin D2, the form found in plant
foods and some vitamin supplements, and vitamin D3, the form produced by
the body from exposure to sunlight and present in animal sources and
other vitamin supplements. Both forms have been shown to have health
If you believe you are at risk for vitamin D deficiency, consult your
doctor who will evaluate your symptoms (if you have them), lifestyle and
other factors to determine the need to be tested.
This article is for general information only and not intended for
medical advice. If you think you might have vitamin D deficiency you
should discuss your concerns with your doctor.
For more information, call 1.866.CALL.MLH.