This column is the first in a series on nutritional supplements and the existing medical information and recommendations regarding them.  I selected to begin with Vitamin D because of the interest and confusion regarding it.

Vitamin D levels represent  the total amount from diet and the conversion in the skin from sunlight exposure. The average daily intake in US is 200IU/d..  The amount of Vitamin D from sun exposure is dependent on race, season, location, age, clothing, and sunscreen use. Obesity is associated with lower Vitamin D levels.  In addition, there is a natural decline in Vitamin D levels by 20% from late summer to midwinter.

Vitamin D is important for bone mineralization and the reduction of fractures. Low levels are also associated with atherosclerotic heart disease, diabetes, osteoporosis, decreased muscle strength, and an increased risk of falls in the elderly. There may be an association with cancers such as colon and pancreatic cancers although more studies are needed.

Many recent reports note Vitamin D levels of less than 30ng/ml are considered low and may be at risk of the above health issues. At the 30ng/ml level, up to 80% of the US population has insufficient levels of Vitamin D.

In 2011, we can say that inadequate levels of Vitamin D either from poor diet or sun exposure is a substantial public health issue.  With the variability and health issues related to sun exposure, dietary supplementation becomes even more important.  The recommended optimal daily dose is 600IU-2000IU, not to exceed 4000IU daily.

Julian Rowe, MD, MPH, FACOG