Canadian adults are at risk of a vitamin D deficiency and therefore more prone to osteoporosis and fractures.
The findings, coupled with those of other recent reports, indicate that the recommended intake of vitamin D should be higher than the current 200 international units (IUs) for adults in Canada and the United States.
Blood levels of vitamin D and hormones that help to synthesize the vitamin were measured, but calcium intake was not assessed.
More than one third of the group had blood levels of vitamin D that fell below optimum levels at least once during the year, but the actual proportion of adults with insufficient blood levels of vitamin D may be even higher. The study relied on a conservative threshold for vitamin D in the blood and was conducted in a city with one of the highest levels of sunlight exposure in Canada.
Regardless of season, blood levels of vitamin D were lowest among elderly adults, who are at higher risk of the brittle-bone disease osteoporosis.
The findings support those of other studies on adults living in countries at higher latitudes, where people may not get enough wintertime sunlight to trigger the conversion of the vitamin D precursor in the skin.
The darker a person's skin, the more difficult it is for him or her to obtain adequate vitamin D via sunlight.
Canadian Medical Association Journal June 11, 2002;166:1517-1524 (Free full-text article)
This study, as you can read in the more detailed article accessible from the link above, used a cut-off level of only 25 for the Vitamin D. The preferred level they suggest is over 32. In an earlier article I posted on vitamin D testing, you will find the ideal vitamin D level is actually between 50 and 60. Be very careful with levels above 60, as you can have soft tissue calcification.
I also warn that if you take vitamin D supplements like cod liver oil but stop them in the summer, the sun can cause toxic vitamin D levels. This is exactly what happened to me. At the beginning of May, my vitamin D levels were perfect, so I stopped my cod liver oil and took no other vitamin D supplement.
I sunned myself about three times a week, however, and in early July my level had risen to 75 -- definitely in the toxic range. Out of the hundreds of patients I have measured, I am the only person showing toxic vitamin D levels. I believed the feedback from the sun would prevent levels from rising excessively, but apparently this is not true if one has vitamin D stores from an external source, like a vitamin or cod liver oil.
The bottom line is that vitamin D is important and can produce massive health benefits and prevent many illnesses, but you need to monitor your dose with blood levels. If you are already in the ideal range, try to avoid excess exposure to the sun.
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