Helps prevent hip and other bone fracturesOne of D vitamin's primary functions is to regulate the body's absorption of calcium in the body, making it a key player in the prevention of bone softening diseases such as osteoporosis and osteomalasia. A 2009 study by the University of Pittsburgh determined that low levels of the vitamin can increase post-menopausal women's risk of hip fracture by as much as 70%.

May help protect against many forms of cancer, including breast cancerA 2008 study by the German Cancer Research Center, which monitored almost 2,800 post-menopausal women, concluded that women with very low blood levels of the vitamin had a significantly higher risk of developing breast cancer than those with adequate levels.

In addition, the American Journal of Clinical Nutrition reports that in four-year clinical trial involving 1,179 healthy post-menopausal women showed that improving calcium and vitamin D nutritional status substantially reduced all-cancer risk in postmenopausal women.

Deficiencies linked to bacterial infections in pregnant womenAnother University of Pittsburgh study indicated that there was a strong correlation between low levels of the vitamin and the incidence of bacterial vaginosis in the more than 460 pregnant women participating in the research. Bacterial vaginosis is one of the primary causes of premature delivery and fetal death.

A total of 41 percent of the study participants were diagnosed with bacterial vaginosis, and 93 percent of the women with the infection had insufficient levels of the vitamin. It was further observed that as blood levels of the vitamin rose, the incidence of infection decreased.

May help prevent and treat depressionIt is known that the vitamin plays a key role in a number of neurological and hormonal processes, and feelings of depression are identified as one of the symptoms of D vitamin deficiency. This connection may be of increasing importance to older women, because the body's ability to manufacture D vitamin decreases as we age.

The importance of the vitamin to mood was established in a 2008 study by the University of Amsterdam, which showed that older people with low levels of the vitamin were more likely to be depressed. The researchers said that while additional study is warranted to determine whether low levels of the vitamin were the cause of depression or a side effect of it, they observed that the correlation between low D vitamin levels and depression were unmistakable.

Boosts energy and improves physical performanceFeelings of fatigue are among the symptoms of D vitamin deficiency, and recent research by the Wake Forest University School of Medicine pinpoints the importance of sufficient levels of the vitamin for improving performance among older people.

The study analyzed data from 976 people aged 65 and older. The study found that physical performance, which included factors such as walking speed, grip strength, and ability to rise from a sitting position to standing, was 10 percent lower among participants with deficient blood levels of the vitamin.