In a recent post on vitamin D I referred to the “sun deficient zones” of the earth, which are the areas farther from the equator in which people do not get enough sun during winter months to produce the needed amounts of vitamin D from their skin. I may have confused some of you when I defined the “sun deficient zone” as being outside the latitudes of 37 degrees from the equator. Let me try and explain it better.
Visualize a line running east and west across the U.S. roughly from San Francisco to Las Vegas, St Louis and on to Washington DC. If you live north of this line, in cities such as Chicago, Toronto and New York, you are in the “sun deficient zone” and are at risk for all the vitamin D-preventable diseases I mentioned in a previous blog.
In Asia this line runs just north of Tokyo and Seoul, so Shanghai, Hong Kong, Taipei, Kuala Lumpur and Singapore all have healthy sun all year round. In the southern hemisphere, visualize a line running through Melbourne and Auckland. All the areas north of this line are in what we might call the “sun-sufficient” zone. Therefore most of New Zealand is in the sun deficient zone whereas Australia is not.
Virtually all of Europe is sun deficient in winter. Even sunny Italy and Greece are located where there is not enough sun in the winter months to produce adequate vitamin D. In contrast, virtually all of South America and all of Africa are in the sun-safe zone all year.
Proper sun exposure is so important. My guideline is approximately 20 minutes in midday sun most days of the week when you are in a sun-sufficient zone. For more information on sun exposures, see the Safe Sun Tables in Dr. Michael Holick’s book, The UV Advantage. He also discusses the effects of other factors, such as skin type, time of day, etc.
Although the consequences of vitamin D deficiency are extensive, it’s hard to know if you are deficient. It’s been said that if you press on your sternum (breastbone) and it hurts, you may be suffering from a vitamin D deficiency, but otherwise you need laboratory testing to determine what your blood levels are. Becoming deficient in vitamin D happens slowly, and recovery comes slowly, which is another reason why daily supplementation is important, especially if you live in a “sun deficient” zone.
As I promised, here are more study results confirming that sun deprivation increases the risk of degenerative disease.
1. Multiple sclerosis is about five times more likely to affect you if you live in North America or Europe compared with the tropics.
2. Diabetes is very rare in equatorial regions, while Finland has the world’s highest incidence.
3. The cancer death rate is 150 percent greater in people living in high latitudes than in the tropics.
Sun deficient zone 3 2 12/4/2009
