Author: Rashi Venkataraman
Institution: Carnegie Mellon University
Date: March 2008
In elementary school, children are taught the importance of milk and how it can help them grow strong and healthy bones. Although this tutorial may seem simple or even silly, it is important to realize that not all children receive this lesson from a young age. In fact, some may never receive this information at all.
Image Courtesy: Oregon State University
Functions of Vitamin D
Vitamin D plays myriad of roles in our body. Once metabolized in the liver and kidney, its principal role is in calcium homeostasis. Essentially, the work of vitamin D mimics that of a watchdog in the body. As soon as the calcium level drops, vitamin D increases the efficiency of the intestine to absorb more calcium, while at the same time, signaling osteoclast precursors to mature and dissolve the calcium stored in bones. Either function restores calcium levels in the body. Other functions of vitamin D include regulation of cell growth (and therefore, cancer prevention), immune function (through immunomodulation), as well as overall muscle and bone health.
Sources of Vitamin D
Major sources of vitamin D include fortified dairy products and natural sunlight. Although most doctors place a huge importance on the dietary sources of vitamin D, over 90% of the vitamin D that your body receives is actually harnessed from natural sunlight (8). Simply put, the ultraviolet (UV) rays from the sun initiate vitamin D3 synthesis in the skin. Many scientists have proved the relation of UVB photons from the sun with vitamin D synthesis in our body. Their research includes variables like skin pigmentation, sunscreens, age of skin, location, and even zenith angles from the sun.
Image Courtesy: Massachusetts General Hospital
Vitamin D and sunlight
Scientists first observed the correlation between sun and vitamin D during the time of industrial revolution, when children living in sunless narrow alleys showed symptoms of rickets (growth retardation, bowing of legs, etc). By 1700, studies estimated that over 90% of children in the industrialized cities of North America and Europe had some signs of rickets. A comparative trend was the relative absence of rickets in the developing world (Palm 1890). These observations revealed the connection between vitamin D and natural sunlight.
A recent problem confronting the issue of vitamin D and natural sunlight deals with the use of sunscreens for those that go sunbathing in the summer. In 1987, Matsuoka found that even a sunscreen with an SPF of 8 (generally, SPF of 15 is the minimum that is encouraged) can reduce the UVB absorption by your skin by close to 98%, thereby decreasing the synthesis of vitamin D3 by 98%1. Similarly, Michael Holick, a researcher at Boston University's School of Medicine argued that the public health campaign for anti-skin cancer actually made vitamin D deficiencies much worse off because it did not advocate a simultaneous increase in consumption of vitamin D while it promoted less time in the sun (2).
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Vitamin D and religious customs
While laboratories helped researchers and scientists to determine the role of vitamin D deficiency in many problems of the body, public health reports have also confirmed the association. For example, in one study conducted in Middle Eastern (3) and other predominantly Muslin nations (4), researchers found a high prevalence of rickets among children (3-18 mos) reflecting the vitamin D deficiency. However, those countries being the tropical ones, the lack of natural sunlight could not be justified as the cause of deficiency. This pushed scientists to look for another explanation for the problem. Eventually, they found that most of the women in these nations cover themselves in veil owing to religious and social customs, which deprived them of sun and vitamin D (5). So, the women were themselves vitamin deficient which they passed on to their children through their breast milk.
Other factors for Vitamin D deficiency
Other factors besides a lack of sunlight exposure can also cause the deficiency. In the 1970s, more cases of rickets were seen among South African children aged from four to seventeen years of age. Because of South Africa's tropical climate and abundance of natural sunlight, a direct correlation between a vitamin D deficiency and lack of exposure to sunlight could not be drawn. In addition, because the children were older in age, there was no question of the deficient status being transmitted from the mother. A research team found that their diets were relatively low in dairy products (perhaps due to a lack of sanitation & refrigeration facilities required for the majority of dairy products) (9). However, after treatment with calcium supplements, the problems associated with rickets seemed to go away quite efficiently (6). Similar trends were seen in Nigeria and Bangladesh.
A scenario in developed countries
Perhaps what is more frightening is the recent result of a study conducted at the Children's Hospital of Philadelphia. Here researchers found that even otherwise healthy children and adolescents have low vitamin D levels, with African American children above the age of nine being the most common. The study which appeared in the American Journal of Clinical Nutrition measured 25-hydroxyvitamin levels a measure of overall vitamin D level in the body - in the blood samples from over 350 healthy children between the ages of six and twenty-one. It was found that more than half of the children had an inadequate level of vitamin D while nearly two third of them had levels that were in the low range in the wintertime. Babette Zemel, the lead researcher of the study claims "Vitamin D deficiency remains an under-recognized problem overall, and is not well studied in children (7)."
Although it is not to belittle the problems in the third world, the recent trend in vitamin D deficiency in younger people in the United States and Europe is definitely something that should raise eyebrows in health circles. For the most part, these children are not barred access to balanced meals or sunlight exposure; at the very least the public schools that they attend should provide them with the necessary serum 25(OH)D levels required. However, the problem still exists, telling us that this problem is a global one affecting those from the most privileged communities to the unpriveleged ones.
So, what's the solution?
Perhaps the best way to combat vitamin D deficiencies is to teach children and mothers to take measures to avoid it. It is important that they understand the importance of dietary sources, sunlight exposure and supplements. It is also crucial that the government steps up to aide those groups who are facing the most serious predicament mainly the African Americans and the elderly.
References:
1 Matsuoka LY, Ide L, Wortsman J, MacLaughlin JA, Holick MF. Sunscreens suppress cutaneous vitamin D3 synthesis." Journal of Clinical Endocrinology & Metabolism. 1987; 64:1165-8.
2 Allen S. "Vitamin D Deficiency tied to host of dangers." The Boston Globe. 2004 Dec 30. Available from: http://www.boston.com/news/globe/health_science/articles/2004/12/30/vitamin_d_deficiency_tied_to_host_of_dangers/?page=full
3 Bassir M, Laborie S, Lapillonne A, Claris O, Chappuis MC, Salle BL. "Vitamin D deficiency in Iranian mothers and their neonates: a pilot study." Acta Paediatr. 2001;90:5779.
4 Molla AM, Badawi MH, Al-Yaish S, Sharma P, el-Salam RS, Molla AM. "Risk factors for nutritional rickets in children in Kuwait." Pediatric International. 2000;42:2804.
5 Pettifor, John M. "Nutritional rickets: deficiency of vitamin D, calcium, or both?" American Journal of Clinical Nutrition. 2004;80(suppl):1725S9S.
6 Pettifor, John M, Ross P, Wang J, Moodley G, Couper-Smith J. "Rickets in children of rural origin in South Africa: is low dietary calcium a factor?" Journal of Pediatrics. 1978; 92:3204.
7 McCool, Joey M. "Low vitamin D levels may be common in otherwise healthy children." Children's Hospital of Philadelphia Press Release.
8 Holick, M.F. "Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancer, and cardiovascular disease." American Journal of Clinical Nutrition. 80:6. 1678S-1688S. December 2004.
9 Pettifor, JM; Ross, P.; Wang, J.; Moodley, G.; Couper-Smith, J.; "Rickets in children of rural origin in South Africa: is low dietary calcium a factor?" Journal of Pediatrics. 1978; 92:3204.
Written by Rashi Venkataraman
Reviewed by Suvash Shrestha
Published by Pooja Ghatalia.