The vitamin D story begins with the evolution of human skin color in Africa. The current hypothesis is that early humans had more of the dark pigment melanin in their skins to provide protection against intense sunlight. But melanin can also block the ultraviolet radiation that triggers vitamin D production in the skin. In Africa, we humans produced the right amount of Vitamin D for our health. As we migrated out of Africa to live at higher latitudes, natural selection favored those with lighter skin, who could absorb more vitamin D from sunlight. People with darker skins were more likely to have Vitamin D deficiency and develop rickets. Women with rickets often have a deformed pelvis and have great trouble giving birth, leading to an evolutionary disadvantage. In the early 20th century (before vitamin supplementation) blacks in the US were 2-3 times more likely to suffer from rickets as whites. Dark-skinned people in higher latitudes need to be exposed to about 6 to 10 times as much sunlight as white-skinned people for the vitamin D in their blood to reach acceptable levels.
Vitamin D, formed on the skin with sun exposure, is a fat soluble vitamin essential for maintaining many body systems. Virtually all of our cells have receptors for Vitamin D. Current studies show the following:
*Osteoporotic fractures - Women who take calcium and vitamin D supplements have been shown to have a lower risk of fractures in the hip and other areas. Levels of supplementation higher than 400 IU daily were needed to achieve these results. D also helps to prevent tooth loss.
*Muscle strength -Vitamin D is helpful in promoting muscle strength and decreasing muscle pain. Recent studies show that vitamin D decreases falls in the elderly.
*Weight Loss - several studies show that overweight people on diets lose more weight when they take calcium and vitamin D. There is much current interest in adding Vitamin D and calcium supplements to all weight loss regimens.
*Heart disease - Low levels of D is associated with an increased risk of heart disease, high blood pressure, insulin resistance and systemic inflammation
*Cancer – a study from University of California San Diego has shown that higher serum levels of vitamin D are associated with substantially lower rates of colon, breast, ovarian, renal, pancreatic, aggressive prostate and other cancers. The authors of this study conclude that raising serum D in the population to optimum levels (40 to 60 ng/mL) could prevent approximately 58,000 new cases of breast cancer and 49,000 new cases of colorectal cancer each year, and three fourths of deaths from these diseases in the United States and Canada, (This is an astounding theory, and if even partially true it could prevent a great deal of suffering.)
* Autoimmune disease Adequate vitamin D levels may decrease the risk of autoimmune diseases such as type 1 diabetes, multiple sclerosis and rheumatoid arthritis.
* Memory loss with aging A recent English study showed that seniors with the lowest levels of vitamin D were twice as likely to have cognitive impairment (memory, attention span and orientation in time and space) as those with the highest levels of vitamin D. A study from Tufts University in Boston showed that seniors with higher levels of vitamin D did better with planning, organizing and thinking abstractly, and also were less likely to show damage to small blood vessels in the brain.
*Respiratory infections people of all ages with low levels of D are more at risk for colds and other respiratory infections, including tuberculosis. This finding is more important in the current flu season.
*Seasonal affective disorder (winter blues) and depression - Studies are beginning on the use of Vitamin D for SAD, which may be more effective than light therapy.
*Vitamin D deficiency in the US More than 75% of Americans have less than optimum levels of D according to a nationwide nutrition study from 2001-2004. Increasing skin protection from sunburns, less outdoor activity, and declining milk consumption may explain the decrease. Also low levels of vitamin D are associated with obesity, which has been increasing in this country.
How to get enough Vitamin D - Since Vitamin D plays such an important role in health, what should you do to protect yourself? You can start by having your health care provider order a test for a blood level of 25 hydroxy vitamin D. A level above 30 ng/ml is desirable, and 40-60 ng/ml is considered optimum. To achieve this level without high sun exposure, which can carry risks of skin cancer and skin aging, most adults in our area need to supplement with at least 1000 IU daily, and may need more. You can increase this amount until you have the desirable blood level of D. If getting a blood level for D is not practical for you, you will be safe with 1000-2000 IU daily. The researchers at UCSD (see above - Cancer) suggest 2000 IU daily, and affirm its lack of risks.. We form very little Vitamin D on our skin between October and March at this latitude. People with darker skin absorb Vitamin D from the sun more slowly, and may need higher levels of supplementation.
: Sadja Greenwood, MD, MPH –back issues at on this blog