By Sheldon Margen and Dale A. OgarVitamin D is actually a hormone. It is manufactured by the body to help with utilization of calcium and phosphorous.
Surprisingly, most people don't even need to get their daily requirement of vitamin D from food since it is manufactured by skin cells that have been exposed to sunlight. And it doesn't take very much sunlight, either. Most people only need 10-15 minutes of sun on their arms and face two or three times a week because vitamin D is fat-soluble and can be stored for months in the body.
In the good news/bad news department, sunscreen, which, protects against skin cancer, may also keep the body from producing enough vitamin D.
In the body, vitamin D helps build bones and teeth, and probably helps boost the immune system. In children, a vitamin D deficiency can cause a condition known as rickets, in which the bones don't form properly. In adults, a deficiency may contribute to osteoporosis. There is also some evidence that the death rate from certain cancers, including breast, ovarian and prostate, is higher in people who have little or no sun exposure.
The people who are most likely to be deficient in vitamin D are those who are housebound and get little sun; vegans, who eat no animal products; and the elderly who may not get out much or drink much milk. Dark-skinned people (who need longer sun exposure to get enough vitamin D) and people who live in northern climes, where sunlight is scarce in the winter and temperatures require layers of clothes, need to make sure that they take in enough vitamin D.
A good multivitamin is sufficient to insure your needs. Most contain 400 IUs (International Units) of vitamin D. It is almost impossible to get too much vitamin D from a combination of sunlight, food and a multivitamin. However, individual vitamin D supplements are another story. You must be very careful with them. Above 2,000 IUs a day, and you risk kidney stones, kidney failure, weakness of the muscles and bones, and a host of other problems. As people age, they seem to need more vitamin D, and the recommended daily intake rises. Adults under 50 need about 200 IUs; those over 60 should get 400 IUs, and once you're over 70, you need about 600 IU. Many people in their 60s -- and everybody over 70 -- should take a multivitamin containing vitamin D. The food sources of vitamin D are somewhat limited but include fatty fish, such as salmon and sardines, egg yolks and fortified cereals. The best dietary source for vitamin D is milk, which is fortified with enough to provide 100 IUs in just a cup. Yogurt and cheese are not good sources since they are not made with fortified milk. Milk, for all of the controversy that sometimes surrounds it, does have amazing nutritional credentials. However, the high fat content of whole milk has made it difficult to include in a heart-healthy diet for most people over the age of 2. The good news is that it is possible to get all the value of milk without the fat. None of the valuable calcium, protein or vitamin D is lost by lowering the fat content of milk. In fact, the lower the fat content, the more calcium milk contains.
Because vitamin D helps the body absorb calcium, a food like milk, which is loaded with calcium and fortified with vitamin D, can be an extremely important tool in the fight against brittle bones. This is a process that needs to be started early in life. The requirement for calcium is greatest between the ages of 9 and 18, when youngsters lay down almost 40 percent of their total adult bone mass. Studies show that 90 percent of adult women fail to get enough calcium in their diets. Teenagers are also at high risk for calcium deficiency. Dark-green, leafy vegetables are the only other good food source of calcium. Kale is one such vegetable, but you'd need 2 cups of cooked kale to equal the calcium in one glass of milk. Lactose-free milk also contains calcium and is fortified with vitamin D. If you don't like plain milk, try making a fruit milkshake by adding strawberries, peaches or frozen bananas to 2 cups of skim milk or lactose-free milk, with a dash of sugar. Blend the ingredients, and sprinkle with a little cinnamon. These shakes are so good, it's hard to believe how nutritious they are. Sheldon Margen, M.D., is a professor of public health at the University of California at Berkeley. Dale A. Ogar is managing editor of the University of California at Berkeley "Wellness Letter." They are the authors of "The Simply Healthy Lowfat Cookbook," "The Wellness Lowfat Cookbook" (1994) and "The Wellness Encyclopedia of Food Nutritution" (1992). - - - - -
Source: Health & Wellness
