July 01, 2007
Sun No Guarantee Of Adequate Blood Vitamin D

A population of adults in Hawaii who averaged about 29 hours a week of sun exposure still mostly did not have an optimal amount of vitamin D in their blood.

Participants: The study population consisted of 93 adults (30 women and 63 men) with a mean (SEM) age and body mass index of 24.0 yr (0.7) and 23.6 kg/m2 (0.4), respectively. Their self-reported sun exposure was 28.9 (1.5) h/wk, yielding a calculated sun exposure index of 11.1 (0.7).

Main Outcome Measures: Serum 25(OH)D concentration was measured using a precise HPLC assay. Low vitamin D status was defined as a circulating 25(OH)D concentration less than 30 ng/ml.

Results: Mean serum 25(OH)D concentration was 31.6 ng/ml. Using a cutpoint of 30 ng/ml, 51% of this population had low vitamin D status. The highest 25(OH)D concentration was 62 ng/ml.

I wonder what their racial and age breakdown was. First off, darker skinned people will make less vitamin D from a given amount of sun exposure. Second, as skin ages it very likely becomes less efficient at harnessing sun to make vitamin D.

Another report on this study says only about 22 of those hours were without sunscreen on average. But 22 hours a week is a lot more than people get in colder climates except maybe during the summer times.

Another recent study by Paul Lips and colleagues using subjects from the Longitudinal Aging Study Amsterdam found that blood vitamin D below 20 ng/ml was associated with a more rapid decline in physical performance among the elderly.

Conclusions: Serum 25-OHD concentrations below 20 ng/ml are associated with poorer physical performance and a greater decline in physical performance in older men and women. Because almost 50% of the population had serum 25-OHD below 20 ng/ml, public health strategies should be aimed at this group.

This doesn't prove a cause and effect. It could be that sicker people get out into the sun less. Or people who get out more exercise more and therefore do a better job of maintaining muscle mass as they age.

Another study from 2005 found that even women receiving anti-osteoporosis therapy do not have enough vitamin D.

Conclusions: More than half of North American women receiving therapy to treat or prevent osteoporosis have vitamin D inadequacy, underscoring the need for improved physician and public education regarding optimization of vitamin D status in this population.

Think about what this says about doctors. These women have crumbling bones. Did the doctors prescribe vitamin D to boost their deficient blood vitamin D levels? Probably not. Yet vitamin D is essential for good bone health.

Share |      Randall Parker, 2007 July 01 05:49 PM  Aging Diet Studies

rsilvetz said at July 1, 2007 7:07 PM:

We're missing something here. Basically these folks are getting 4 hours of sun per day. That should be much more than enough to get optimal levels of Vitamin D in their bloodstream.

The self-reported aspect of this bothers me the most. I would rather have literally paid them to be lizards for 10 days straight for 4/day with start/end Vitamin D levels.

Take home message remains the same from our previous Vit D excursions. Supplement at the limit, don't lose sleep over it and blood test once to confirm you are at optimal levels.

WebDoc said at July 2, 2007 10:33 PM:

Vit D is always recommended along with Calcium in treatment of Osteoporosis. 200 IU are in each combo pill and with a daily vitamin results in about 800 IU daily. Untill very recently there was little consensus in recommending higher doses. We clearly need to follow Vit D levels in elderly and perhaps need daily doses 5 times what we currently recommend. Many recent articles have demonstrated the need for higher replacement doses. Somewhere between 800 IU and 5000 IU is the right dose. We don't have enough information to recommend replacement levels in the thousands untill we see more data. I am checking 25 OH Vit D levels in many more patients than ever before.

Dragon Horse said at July 3, 2007 6:21 AM:


Just curious. Do you know if vitamin D/calcium levels have been shown to effect IQ in a significant way?

JEmerson said at July 3, 2007 9:31 PM:

I'm about as pale as it's possible to be, and this is one of the few times I've actually looked at it as a health benefit. Assuming this is true, my forced supplementation of vitamin D means I may have been getting healthier levels than my sun worshiping friends and family.

rsilvetz said at July 4, 2007 12:39 AM:

Don't count them out yet JEmerson. The preponderance of the evidence does not favor this trial. Extensive review at my old Alma Mater (Boston U) suggests that sun intake is all that is needed. It is unwise to have humans self-report because human self-deception is very high, so one shouldn't really trust this study. Nonetheless, we also have sufficient evidence to say that a couple thousand possibly upto 10K units of Vitamin D are safe, so supplementation is a definite option here.

Randall Parker said at July 4, 2007 9:19 AM:

Dragon Horse,

Don't know whether vitamin D has any IQ effects. Interesting question though.

Post a comment
Name (not anon or anonymous):
Email Address:
Remember info?

Go Read More Posts On FuturePundit
Site Traffic Info
The contents of this site are copyright