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At the height of the Industrial Revolution, there arose a mysterious disease that plagued children in both Northern European and U.S. cities. This disease left children with weak bones, bowed legs, and growth retardation, and in adults it caused pelvic bone deformity so severe that giving birth vaginally was impossible. Birth by Caesarian section became widespread in Britain as a consequence of this bone-deforming disorder, which became known as “rickets” in children and “osteomalacia” in adults. After a 270-year search, in the first quarter of the 1800’s, the cure was found in two seemingly different substances: sunlight exposure and small amounts of cod liver oil.
The “first wave” of vitamin D awareness (early 1900’s to mid-1990’s)
Vitamins are essential biological compounds that cannot be synthesized in the body and must be consumed in the diet. Identification of the substance in cod liver oil that cured bone-deforming rickets led to the classification of this compound as a vitamin — vitamin D. We now know, however, that vitamin D is not so much a “vitamin” as it is a “pre-hormone” produced in skin that is exposed to sunlight. Exposure to a specific spectrum of solar ultraviolet radiation causes a pre-vitamin D compound to be synthesized, which is converted into vitamin D within 1 to 2 days, and later transformed by the liver and kidneys into the active vitamin D hormone.
Throughout our evolution, we humans have obtained the vast majority of our vitamin D from exposure to sunlight. With abundant sunlight exposure, we do not need to consume food sources of vitamin D. In fact, few human foods, aside from fish oils, contain significant amounts of vitamin D (see our vitamin D food chart). Even today with our vitamin D fortified foods, 80% or more of our vitamin D is produced from sunlight exposure.
In the early 1900’s, the discovery of the vitamin D factor in cod liver oil that cured rickets and osteomalacia was a triumph of early nutrition science. Stemming from this success, the “first phase” of vitamin D awareness established the need for vitamin D at the minimal amount that could prevent bone-weakening rickets. The tiny amount of 100 International Units (IU) per day was enough to prevent rickets and for decades was held to be an appropriate and adequate vitamin D intake.
This “first wave” of vitamin D awareness also brought the realization that vitamin D was fat soluble and stored in the body, and thus had a potential for toxic accumulation. For various reasons, vitamin D toxicity became an issue of exaggerated concern, the extent of which is only now becoming evident. Looking back, scientists now realize that vitamin D toxicity is rare and generally occurs from extremely high oral intake, never from sunlight exposure. The early cases of vitamin D toxicity that formed the basis for safety concerns generally involved impurities in vitamin D production, the use of synthetic vitamin D analogues, accidental use of extremely high doses, or individuals with vitamin D hypersensitivity.
Better Bones guidelines for sunlight exposure
- Short periods, 15-20 minutes daily, of near full-body exposure are best for light-skinned people (without sunscreen).
- Use sunscreen after this initial period if necessary to avoid a sunburn.
- The useful ultraviolet rays are strongest between 10 am and 2 pm.
- Very dark-skinned people require 4-6 times more sunlight exposure than light-skinned people.
- In northern or southern latitudes distant from the Equator, longer exposure is needed, especially during the spring and fall.
- In climates of the northern or southern latitudes distant from the Equator, very little or no vitamin D is produced in the skin during the winter months.
The “second wave” of vitamin D awareness (mid-1990’s to 2008)
By the mid-1990’s, a silent revolution had begun. A handful of insightful scientists began challenging our most basic assumptions about vitamin D and began to explore the full importance of this substance for human health. Most importantly, they began to question what might be the optimal level of vitamin D for human health, as opposed to the minimal level used to prevent rickets and osteomalacia. This in turn led to a long overdue critical analysis of both the potential benefit and potential toxicity of vitamin D. Well-respected researchers, including Dr. Reinhold Vieth of the Mt. Sinai Hospital, University of Toronto and the American “calcium guru”, Dr. Robert Heaney of Creighton University in Omaha, Nebraska, blazed this exciting new scientific trail. Today, hundreds of scientific papers are published each month, and we are learning more about the power of vitamin D than anyone could have imagined even twenty years ago. An updated discussion of the wide-ranging health benefits of vitamin D can be found in my article, “Vitamin D: Its benefits are more than ever imagined,” and on many websites, including www.grassrootshealth.org, www.sunarc.org,www.vitamindcouncil.org, and www.vitamin-d.com.
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I’m Dr. Susan Brown. I am a nutritionist, medical anthropologist, writer, and speaker. Get my free weekly newsletter here.