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Is vitamin D deficiency hurting you?
Is your child getting enough of vitamin D? What if not? What about you? And what is "enough", anyway? As we are becoming increasingly aware of its importance to health, answering this questions becomes more pressing. Two recent studies found that vitamin D deficiency in both, children and adults is rather common. The real picture, though, is likely worse than what the studies present.
After each next study, vitamin D seems to be more important for health - and we seem to be more deficient in it than we thought. Two recent studies indicate more specifically how widespread is this deficiency in both, children and adults - and what are some of its health consequences.
The first study (Kumar et al, Pediatrics 9/2009, published online August 3) set as objective to establish prevalence vitamin D deficiency - measured as serum 25-hydroxyvitamin D, or 25[OH]D level (primary vitamin D metabolite, accepted as indicator of body's vitamin D status) - and associations between this deficiency and cardiovascular risk factors in children and adolescents.
Results obtained from nationally representative sample of 6,275 children and adolescents aged 1 to 21 years from the National Health and Nutrition Examination Survey 20012004, showed that
vitamin D deficiency is common among American
and that it is associated with adverse cardiovascular risks.
More specifically, defining 25[OH]D level below 15ng/ml (nanograms per milliliter) as deficiency, and between 15 and 30ng/ml as insufficiency, the study found that 9% of the sample was deficient, and 63% with insufficient vitamin D level. The segment of the sample with by far the greatest risk from deficiency were non-Hispanic blacks -
nearly 22 times higher than the average.
At the lowest risk, 2.5 times lower than the average, were those taking vitamin D supplementation.
Low vitamin D level was associated with elevated parathyroid hormone level - interfering with proper bone formation/regeneration - blood pressure and HD (high-density, "bad") cholesterol on one, and with lower blood calcium levels on the other side, all three increasing the risk of cardiovascular disease.
The other study (Reis et al, Pediatrics 9/2009) also used the NHNES database, but concentrated on 3,577 adolescents. They had the average 25[OH]D level of 24.8 ng/ml, with blacks as a group at the low end with 15.5 ng/ml, Mexican American intermediate with 21.5 ng/ml and whites at the high end with 28 ng/ml. The study found that low vitamin D status was strongly associated with overweight status and abdominal obesity. Also, that 25[OH]D blood level was inversely associated with blood pressure and glucose level.
In all, the risk of metabolic syndrome (increased risk of developing heart disease, stroke and diabetes, as a result of cumulative health/lifestyle factors) was
nearly four times higher
in those in the lowest quartile (<15ng/ml), compared to those in the highest quartile (>26ng/ml).
Results of these studies are only among the latest additions to already voluminous research data consistent in finding vitamin D vitally important for health preservation and/or, at the same time, commonly deficient in the general population. Obviously, this is a no good combination, so let's try to throw some light on the causes and possible remedies for this problem.
With vitamin D naturally low in foods, the main cause of deficiency appears to be the lack of sunshine exposure. Studies have shown that light-skinned individuals can produce equivalent of ~20,000 IU of vitamin D2 in as little as 15-20 minutes of total (all, or nearly all skin) summer sun exposure (Holick 2004 and 2006, Heaney et al. 2003, also Matsuoka et al 1989, Haddad et al 1993). Dark-skinned individuals may produce less than 2/3 as much, but it is still plenty according to even most demanding views.
After this level of the vitamin is produced, the body averts further accumulation by converting vitamin D to various inactive metabolites.
It was also established that 5 to 30 minutes (depending on time of day, season, latitude, and skin pigmentation) exposure of arms and legs to sunshine, between 10AM and 3PM twice a week is usually sufficient for the body to produce enough vitamin D to satisfy its needs (Holick 2006, Sato et al 2005, Jones and Dwyer 1998, Reid et al 1986).
However, abundant sunshine exposure may not be enough to result in 25[OH]D blood level above 30 ng/ml. A study of 93 adults in Honolulu, Hawaii, reporting average sun-exposure of over 4 hours a day, found that
only about half of them had more than 30ng/ml,
with the highest level being 62ng/ml (Binkley et al, 2007). About 42% had between 20 and 30 ng/ml, with about 8% below 20 and 4% above 50 ng/ml.
While it is no news that significant segment of population in countries with abundant sunshine (as studies from Lebanon, United Arab Emirates, Australia, Saudi Arabia, India and Turkey show) scores insufficient or deficient on the vitamin D status, with 30-50% of children and adults having 25[OH]D below 20 ng/ml, this study is different in that it concentrates on young (over 18) beachgoers, that actually do get significant sunlight exposure.
Study limitations are dependence on self-reported duration and (skin) extent of exposure, use of sunscreen (blocking UV light needed for vitamin D synthesis in the skin) and partial insight in medication use possibly affecting vitamin D level (only three - phenobarbital, phenytoin and prednisone - were included). Also, other factors such as obesity, skin melanin levels or disturbances in fat absorption/metabolism were not considered.
Yet another factor that did affect nominal study results is the choice of 25[OH]D measurement technique, producing up to 25% lower values than the alternative assay (which measures wider array of vitamin D metabolites). Also, the study took place during Hawaiian winter, when the UV exposure and vitamin D synthesis are at their lowest (comparable to those in Chicago during summer time).
In all, even if the study results may be picturing somewhat more pessimistic picture than what it really is, the overall implication is still that skin exposure to sunshine alone
may not be enough to provide sufficient vitamin D level,
and in some cases not even able to prevent serious deficiency.
This baffling conclusion only adds to confusion: does this mean that, after all those thousands of years, our bodies still haven't developed reliable mechanism for our natural vitamin D production, long time our only significant source of it?
Which vitamin D assay we should use for assessing the status, since nominal difference can be significant?
Why the above study authors advise, based on their results, that supplementary vitamin D intake shouldn't be producing 25[OH]D level over 60 ng/ml, is contradicting many sources that see this level within the optimum range. Some, like Linus Pauling Institute, consider it even sub-optimum, and the government places the level of toxicity at 25[OH]D consistently above as much as 200 ng/ml?
Also, why is it that the government defines vitamin D deficiency as 25[OH]D level below 10 ng/ml, 10-15 ng/ml as insufficiency, and levels above 15 ng/ml as adequate, while the above studies - and by far most of the educated opinions - define insufficiency as levels between about 30 and 15 ng/ml, some even higher?
The following article starts with the the concluding thoughts on the Hawaiian study, expanding on why and how the official indicator of vitamin D status - serum 25[OH]D level - needs to be redefined if it is to have any meaning.