Vitamin D necessary for calcium absorption Cloudy days, sunscreen and certain diseases can all affect the absorption of the vitamin.
More importantly, it is synthesized in the skin after exposure to sunlight.
Calcium cannot be absorbed without vitamin D. It works with other minerals and hormones to promote mineralization of bones (building bones).
If there is a deficiency of vitamin D, a person may develop osteoporosis (thin, brittle bones) or a softening of the bones.
In children this is called rickets and in adults it is called osteomalacia.
Primarily this is due to an inadequate amount of sun exposure to synthesize vitamin D; it is more common the further you are from the equator.
However, complete cloud cover also will decrease the amount of vitamin D by about half and sunscreen with an SPF of 8 and more will decrease it by 95 percent.
A. We can boost vitamin D levels in the winter by taking a supplement once a day or increasing ingestion of foods that contain vitamin D. Also, some researchers suggest that a short exposure to sun --- 15-20 minutes without sunscreen --- will improve vitamin D levels.
Q. What foods are high in vitamin D?
A. Fatty fish and fish oils are the best sources of vitamin D. Cod liver oil has the most, followed by salmon, eel, herring and tuna and sardines in oil.
A. Recently, the recommended dosages have been increased to the following: 200 international units per day for infants, children, pregnant or lactating women and young adults; 400-600 IU/day for those 50-70 years old and 600-800 IU/day for those over 70.
The recommended tolerable upper limits are as follows: 1000 IU/day in infants and 2000 IU/day in all others.