Vitamin D has been the feared “black sheep” of the vitamin family because excessively high blood levels can cause unfavorably high blood calcium levels and, at times, kidney failure. New research documents, however, that the dangers of vitamin D have been exaggerated, and natural vitamin D3 (also known as cholecalciferol) has much less toxic potential than commonly thought. The Canadian vitamin D expert, Dr. Reinhold Vieth, has found vitamin D3 doses up to 10,000 IU per day to be safe in individuals who do not have conditions that predispose them to high blood calcium (such as hyperparathyroidism and acidosis). Further, fully documented cases of toxicity have only occurred with intakes of 40,000 IU per day or more. This low toxicity of vitamin D is not so surprising when we realize that a light-skinned person in tee shirt and shorts outdoors during the summer in New Jersey can produce 12,000 IU of vitamin D within 20 minutes.
Vitamin D is both more important and safer than ever expected, yet as with all fat-soluble vitamins, it is retained in the body and thus doses above 4000 IU, the current U.S. official “Upper Safe Limit” should be used under proper supervision.
While the RDA for vitamin D ranges from 600 to 800 IU per day, it is now clear that most folks need much more. In fact, researchers now estimate that an adult uses about 3000 – 4000 IU vitamin D daily, the vast majority of which is obtained from casual sunlight exposure. Calcium authority Dr. Robert Heaney of Creighton University recently reported that many individuals will need a daily intake of at least 2200 IU in order to maintain adequate vitamin D blood levels, and those prone to deficiency may even require more.
And, how much vitamin D do you need? Well, that depends on many factors like your amount of sunlight exposure without sunscreen (sunscreens with a SPF factor of 8 reduce skin production of vitamin D by 95%), your genetic make-up, diet, current use of nutritional supplements, and your skin color. Skin color is extremely important, with dark-skinned individuals requiring six or so times the sun exposure to produce the same amount of vitamin D as a light-skinned individual. For example, in a New York study, 81 healthy African American women were given 800 IU vitamin D for two years and then 2000 IU for another year. More than 95% of the women were still vitamin D deficient at the end of three months on 2000 IU vitamin D per day, and 40% still had inadequate vitamin D blood levels after 3 years.
Luckily, there exists a simple blood test which can determine your level and define your vitamin D need. This test is the “25(OH)D vitamin D” test. As vitamin D blood level varies by season, it is a good idea to be tested twice a year, once in mid-winter and again in the summer, to determine your need for vitamin D supplementation throughout the year.
We now know that a blood vitamin D level of at least 32 ng/mL (equivalent to 80 nmol/L) is necessary for optimum calcium absorption and for bone protection. A higher blood level of 50 – 60 ng/mL appears to further enhance immune functioning, and the prevention of wide-ranging degenerative diseases including many cancers. (See Vitamin D scientists’ call to action statement at www.grassrootshealth.org/documentation/scientistscall.php.) It is important to have your level tested so you know if your current lifestyle and nutrient and supplement intake are providing you with an adequate amount of this multi-faceted, life-supporting nutrient.
While vitamin D is clearly safer than previously thought, it is always wise to consult with your healthcare professional to determine your specific supplementation program. Individuals with special health concerns and those with disorders such as kidney failure, a history of kidney stones, high blood calcium, hyperparathyroidism, sarcoidosis, oat cell carcinoma, non-Hodgkin’s lymphoma, or leukemia should not use vitamin D supplements unless under clear guidance of their physician.
The ongoing scientific research on vitamin D is amazing with various new and important research articles and clinical trial reports being published each day. As it would appear, nearly every health concern that researchers look at is influenced in one way or another by vitamin D. The best way to keep current on this explosive research is to monitor the major public-interest vitamin D websites. These sites include the following: