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Why The Official Recommended
Intake for Vitamin D is Too Low

Vitamin D has been a natural part of man's experience forever, and 90% of vitamin D is derived from solar ultraviolet-B (UVB) irradiance. The health effects of vitamin D can be and have been determined from a variety of studies including ecological, observational (case-control and cohort), and cross-sectional studies.

Vitamin D helps both to prevent and to treat chronic diseases including many types of cancer, cardiovascular disease (coronary heart disease, stroke, etc.), congestive heart failure, diabetes mellitus (types 1 and 2), osteoporosis, falls, and fractures. It is also effective against infectious diseases including both bacteria and viral infections: bacterial vaginosis, pneumonia, dental caries, periodontal disease, tuberculosis, sepsis/septicemia, Epstein-Barr virus, and influenza type A such as A/H1N1 influenza. The autoimmune diseases include asthma, type 1 diabetes mellitus, multiple sclerosis, and perhaps rheumatoid arthritis.

Pregnancy outcomes are also adversely affected by low serum D levels. 40% of primary Cesarean-section deliveries in the United States are linked to low D levels (9% of births in the United States involve primary C-section), and preeclampsia is also linked to low serum levels of D. In regards to cancer, vitamin D helps cells fit into the organs properly or commit suicide (apoptosis), and also reduces angiogenesis (new blood vessel growth) around tumors and reduces metastasis. For metabolic diseases, the mechanisms include increased insulin sensitivity and insulin production. For infectious diseases, vitamin D induces production of cathelicidin and defensins, which have antimicrobial and antiendotoxin activities.

Due to current lifestyles in the United States, most people do not spend sufficient time in the sun to produce the higher serum D levels associated with optimal health. Black-Americans are particularly vulnerable to low levels due to their darker skin, which reduces the amount of UVB that reaches the 7-dehydrocholesterol in the lower epidermis to produce previtamin D. Black-Americans have a 25% higher mortality rate than White-Americans, and this difference may be explained in terms of lower serum 25(OH)D levels. Solar UVB is an excellent source of vitamin D during about half of the year. The way to take advantage of the sun as a source of vitamin D is to expose as much of the body as possible without sunscreen near solar noon, the time when one's shadow is shorter than one's height, for 10-30 minutes depending on skin pigmentation, being careful not to turn pink or red or burn. ( )

Supplements represent an efficient way to obtain sufficient vitamin D. African-Americans should consider taking 3000 International Units (IU) per day while White-Americans should consider taking 2000 IU/day. The current dietary guideline, approximately 400 IU/day, was based on the amount of vitamin D in a spoonful of cod liver oil, which prevented rickets.

There are few adverse effects of vitamin D. With whole-body exposure to the sun, one can make at least 10,000 IU/day in a short time. Adverse effects such as hypercalcemia have been found in general only for 20,000-40,000 IU/day for very long periods. However, those with certain diseases such as adenoma of the parathyroid gland, granulomatous diseases, lymphoma, sarcoidosis, and tuberculosis, should limit their vitamin D intake or production due to the fact that the body's innate immune system produces too much 1,25-dihydroxyvitamin D in the serum, which can raise serum calcium levels too high.

Several studies have examined how much mortality rates and economic burdens of disease could be lowered if the population had more vitamin D. These studies were for Western Europe, Canada, the Netherlands, and the United States. They generally found that mortality rates could be reduced by about 15%.

During pregnancy and lactation, women should be taking about 6000 IU/day. The current US "Adequate Intake" recommendation is a mere 200 IU/day. Bruce W. Hollis and Carol L. Wagner, Medical University of South Carolina, recently completed a randomized controlled trial vitamin D supplementation for pregnant and nursing women and found that even 2000 IU/day was inadequate, and that there were no adverse effects with 6000 IU/day.

For the text of a Vitamin D Scientists' Call to Action, please go to .

William B. Grant earned his PhD in physics at UC Berkeley. For 15 years he was a physicist at NASA Langley Research Center's Atmospheric Sciences Division. He has authored or coauthored over 180 papers in peer reviewed journals. Since he began his work on UVB/vitamin D and cancer in 2000, the list of vitamin D-sensitive cancers has grown from 5 to at least 16. His paper in Cancer in 2002 identified 10 additional vitamin D-sensitive cancers. Dr. Grant directs the Sunlight, Nutrition, and Health Research Center (SUNARC)

Reference Sources:

February 23, 2010

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