Q. I'm 68 years old and I want to know how much Vitamin D you need to be healthy.

The U.S. Institute of Medicine of the National Academy of Sciences has established Adequate Intake (AI) levels for vitamin D. The daily levels in International Units (IU) for everyone are as follows according to age:

Ÿ Under 50 - 200 IU

Ÿ From 50-70 - 400 IU

Ÿ Over 70 - 600 IU

The recommended upper limit for vitamin D is 2,000 IU a day. Vitamin D can be toxic when taken in higher doses. Vitamin D is included in most multivitamins, usually in strengths from 50 IU to 1,000 IU. Vitamin D toxicity is rare.

There is a greater risk of poisoning if you have liver or kidney conditions, or if you take some diuretics.

There are different forms of Vitamin D. The major forms the ones important to humans are vitamin D2 and vitamin D3.

Vitamin D2 is synthesized by plants. We get vitamin D in our diet. Very few foods in nature contain vitamin D. It is found in eggs, dairy products, fish, oysters and cod liver oil. Foods, such as milk, may be fortified with vitamin D2 or D3. Fortified foods provide most of the vitamin D in the American diet.

Vitamin D3 is synthesized in human skin when it is exposed to sunlight. About 10 minutes of daily exposure to sun is considered enough to prevent deficiencies.

Vitamin D's primary job is to maintain normal amounts of calcium and phosphorus in your blood. Vitamin D helps keep your bones strong. Research suggests that vitamin D may protect us not only from osteoporosis (loss of bone density) but also from high blood pressure, cancer, heart disease, diabetes, multiple sclerosis and psoriasis.

Populations at a high risk for vitamin D deficiencies include the elderly, obese individuals and people with limited sun exposure.

Osteomalacia also known as adult rickets is found in older patients deficient in vitamin D. Osteomalacia causes bone and muscle weakness.

People older than 50 are at increased risk of developing vitamin D insufficiency. As people age, skin cannot synthesize vitamin D as efficiently, and the kidneys are less able to convert vitamin D to its active hormone form.

Recent studies indicate that vitamin D reduces the risk of falling, which is especially dangerous for seniors. However, to obtain the benefits of the vitamin, you must take 700 to 1000 IU a day. These studies buttress other research that has shown that vitamin D improves strength, balance and bone health in the elderly.

Each year, one third of people 65 and older, and one half of people 50 and older fall at least once. Almost one-tenth of these falls puts their victims in an emergency room. Many seniors who fall end up in nursing homes.

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