Vitamin D is a fat-soluble
vitamin. It is called the sunshine
vitamin because it is made in the body when ultraviolet rays from the sun
strike the skin and trigger the synthesis of vitamin D3. Plants synthesize vitamin D2. Both forms of the vitamin must be converted
in the liver and kidneys to the active form, 1,25-dihydroxyvitamin D to be used in the body.
The main function of vitamin
D is to facilitate the body’s absorption of calcium, a major ingredient in bone
formation. A shortage of vitamin D leads
to weak, brittle bones in both children and adults; resulting in diseases known as rickets in children and
osteomalacia in adults.
Promising uses of vitamin D
have been noted in recent research involving reduction of heart attacks. In one study, men deficient in vitamin D were
twice as likely to have a heart attack as men who had adequate levels.
Studies have indicated that
vitamin D status in the body can affect cancer risk. It appears to play a role in the prevention
of colon, prostate, and breast cancer.
Vitamin D levels are lower in the fall and winter months, a time when colds and flu are more prevalent. Observational studies have shown that people with low vitamin D levels are more likely to get these infections or have had a cold or flu in the recent past.
Studies are mixed regarding
whether vitamin D helps reduce weight. A
recent study with laboratory rats showed that rats given vitamin D directly to
the brain had large decreases in food intake and weight when compared to rats
not given the vitamin.
Recommended daily average vitamin D intake recommended by the Food and Nutrition Board is the following :
- Birth to 12 months - 400 IU
- 1 to 13 years - 600 IU
- 14 to 18 years - 600 IU
- 19 to 70 years - 600 IU
- 71 years and older - 800 IU
- Pregnant and nursing women - 600 IU
Optimal vitamin D intake is reported to be much higher,
with 1,000 to 2.000 IU for adults. There
is a growing consensus that vitamin D intake should be at these higher levels
with the widespread prevalence of vitamin D deficiency.
Safe upper limits of vitamin D intake are reported to be
1,000 – 1,500 IU per day for infants, 2,500 – 3,000 IU for children 1- 8 years,
and 4,000 IU for children 9 and
older, adults, pregnant and breastfeeding women.
Taking too much vitamin D can cause weight loss,
increased urination and abnormal heart rhythms.
It can also raise blood levels of calcium which can cause deposits in
tissue and blood vessels and thus damage the heart, blood vessels, and
organs. Increased kidney stone
occurrence has been reported.
Getting
too much vitamin D from food is highly unlikely. Excessive sun exposure will not over produce vitamin D
since the heated skin is thought to degrade previtamin D3 and vitamin D3 as it
is formed.
Before taking vitamin D supplements, you should consult
with your healthcare provider to determine if you require them and how
to take them safely.
