Vitamin D

Also known as: Vitamin D3, cholecalciferol, vitamin D2, ergocalciferol.

Potential uses: Vitamin D helps the body absorb the calcium that is essential for good bone health. This is especially important for menopausal women and women taking an aromatase inhibitor to treat breast cancer, since bone loss is a side effect of the three aromatase inhibitors. Good calcium absorption also can help reduce bone weakening caused by certain chemotherapy medications.

Usual dose: The standard recommendation is that people younger than 50 get 200 international units of vitamin D per day. 400 international units per day is recommended for those aged 50-70, and 600 international units per day is recommended for people older than 70. The typical multivitamin contains 400 international units of vitamin D. Adults who want to reduce the risk of broken bones should take 400-800 international units daily, along with calcium. Vitamin D also is found in food products such as fish, eggs, and fortified milk and cereals. The human body also produces vitamin D when exposed to sun.

Are there any risks? Too much vitamin D -- more than 2,000 international units daily -- can lead to having too much calcium in the blood. Over time, calcium deposits can affect soft tissues such as the heart and lungs. Other risks include kidney stones, nausea, vomiting, confusion, muscle weakness, poor appetite, and weight loss.

What does the research show? For many years, studies have shown that people who are less exposed to sunlight and have lower levels of vitamin D as a result are more likely to develop breast cancer and other forms of cancer. More recently, some research has found that calcium and vitamin D may help protect premenopausal women against breast cancer, but more studies are needed.