Fatty fish are indeed rich in vitamin D, but the fear of mercury pollution keeps many people from eating them.
A lack of vitamin D can for example cause weak and soft bones (rickets), osteoporosis, myasthenia, and immune defects.
Vitamin D is produced in the skin and stored in the body. In winter, when the sun is sparse, the skin hardly produces any vitamin D. Instead, we break into our depots - that is if there are any depots to break into.
Dark-skinned people who live in parts of the world where the amount of sunlight is small will have an even higher risk of getting too little vitamin D unless they take a daily supplement. We should also consider the fact that after the age of 40, our ability to produce vitamin D ourselves is significantly reduced.
How much
Under normal circumstances, 200 - 400 I.U. (5 - 10 mcg.) will be an appropriate daily dose, but individuals who are only exposed to little sunlight may need 400 - 1000 I.U. (10 - 25 mcg.) a day.
Another way of covering your vitamin D need is to take a teaspoon of cod-liver oil every day during the dark half of the year.
In British latitudes, you should get half an hour of sun on our face and lower arms every day from April to October, but our best advice is to take a daily multivitamin-mineral supplement that also contains vitamin D. A broad supplement is more effective than single doses of vitamin D.
