Vitamin D levels found to be falling in Americans

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Vitamin D has gained a reputation for helping to ward off a plethora off ills, including bone disease, cardiovascular disease, cancer, multiple sclerosis and infection. However, while there has been increasing awareness about the multitude of benefits vitamin D can bring, there has also been growing concern that many of us do not have optimal levels of this nutrient in our bodies.

At lest one reason for this concerns that fact that some of our requirements for vitamin D are met by the action of sunlight on our skin. In the last decade or so there has been a concerted campaign to persuade to protect ourselves from the sun with sunscreens and suchlike, less we succumb to skin cancer (including malignant melanoma). As a result of this and perhaps other factors, there is a risk that individuals may end up with lower than ideal levels of vitamin D.

A study published this week in the Archives of Internal Medicine sought to assess the extent of any decline in vitamin D levels in Americans. Vitamin D levels from thousands of individuals were assessed in two time periods: 1988-1994 and then in 2001-2004. What this amounts to is an assessment of vitamin D status in a population over a decade.

For the purposes of the study, the authors defined individuals with sufficient vitamin D as being those with levels of 30 ng/ml (about 75 mmol/L) or more. They defined frank deficiency as a vitamin D level of less than 10 ng/ml (about 25 mmol/L).

Between the two assessments, rates of vitamin deficiency trebled from 2 to 6 per cent.

At the same time, individuals judged to have sufficient vitamin D levels fell from 45 to 23 per cent. What this means is that according to the authors’ criteria, three-quarters of the population studied had insufficient levels of vitamin D at the second assessment.

The study revealed that non-Hispanic blacks and Mexican Americans were significantly more likely to be low in vitamin D than whites. This is perhaps not surprising when one considers that the darker someone’s skin tone is, the less vitamin D is made in the skin for a given amount of sunlight exposure.

There is evidence that maintaining optimal levels of vitamin D, particularly in the winter, requires individuals to take in much higher levels than those currently recommended by our Governments. For more on this, as well the sorts of dosages required to maintain decent level of vitamin D, see here.

Of course another way to boost vitamin D levels is get more sun exposure. Which reminds me that the concerted effort by some to get us to shy away from the sun and slather on the sunscreen is perhaps a major reason why vitamin D insufficiency is becoming increasingly common. When one bears in mind the health risks this might bring, it does get me thinking at that sun awareness campaigns are likely to have one considerably more harm than good. For more the potential hazards of shying away from the sun, see here.


1. Ginde AA, et al. Demographic Differences and Trends of Vitamin D Insufficiency in the US Population, 1988-2004. Arch Intern Med. 2009;169(6):626-632.

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