Your Health: Vitamin D needed for bones, brain

From time to time, I’ll write about various vitamins and how they affect our health. But what exactly is a vitamin?
A vitamin is an organic substance essential in small quantities to normal metabolism. It is found naturally in various foods, but it can also be produced artificially. A lack of vitamins can produce certain diseases.
Vitamin D has received quite a bit of press these days both in medical literature as well as in newspapers and magazines.
Vitamin D is the only nutrient the human body makes itself. Ultraviolet rays from sun exposure interact with a chemical in the skin to form an inactive version of vitamin D, which is then converted in the liver and kidneys into an active version useful to our bodies.
Because people have been warned to wear sunscreen and to limit sun exposure, though, we might not be able to manufacture enough of this vitamin on our own and may need to look for other sources.
Vitamin D can be found in a limited number of foods, including fatty fish, fish liver oils, liver, and egg yolks. Commercial milk products, breakfast cereals and juices are often fortified with low levels of vitamin D. People don’t usually eat enough of these foods to consistently cover their daily vitamin D requirements, though.
The primary benefits of vitamin D for our bodies are these:
• Bone health: Vitamin D helps the body absorb calcium and phosphorus, which are two minerals needed for strong bones. People taking vitamin D have a lower risk of bone fractures and also have been found to have a lower chance of falling in the first place.
• Brain function: People with higher blood levels of vitamin D have higher cognitive performance, including memory and thinking skills.
Low levels of vitamin D, by contrast, have been associatedwith some increased risks: cancer of the colon, breast and prostate; arthritis; diabetes; and infections, such as tuberculosis.
The accepted recommended daily dose of vitamin D is 400 to 600 international units per day. Most common multivitamins contain 400 IU. Momentum is building within the medical community to increase the daily recommended dose to at least 800 to 1,000 IU. From what I can tell, this is a reasonable recommendation. The higher level should help to strengthen bones and muscles and hopefully prevent a variety of diseases, such as those I have mentioned.
• Terry Hollenbeck, M.D., is an urgent-care physician at the Palo Alto Medical Foundation Santa Cruz in Scotts Valley. A doctor with 36 years’ experience, he invites readers to view his previous columns on his Web site, valleydoctor.wordpress.com. Information in this column is not intended to replace advice from your health care professional.  For any medical concern, consult your own doctor.