More Sunlight Cuts Strokes And Arthritis Risk
As reported by Dr John Cannell (Vitamin D Council) (2/13) Sun exposure may cut arthritis risk in women
According to new research led by Professor Elizabeth Arkema and colleagues from
Harvard, increased sun exposure may cut the risk of developing rheumatoid
arthritis. The study, recently published in JAMA, found that more intense sun
exposure was linked with a decreased incidence of rheumatoid arthritis (RA)
among women in the Nurses’ Health Study (NHS).
The NHS established a large cohort in 1976 of over one-hundred thousand nurses
to follow over time. In this recent analysis, the researchers found that women
(ages 30 to 55) living in states with the highest ultraviolet B (UVB) intensity
had a 21% lower risk for RA compared with those living in states with low UVB.
Conclusive evidence? Not so fast. In 1989, the NHSII was established; a second
and different cohort of over 115,000 women. In this cohort, the researchers
found no such decreased risk associated with sun exposure. The risk over 20
years for RA was 0.7% among women in NHS living in states with the highest UVB
compared with 1.2% in those living in states with lowest levels. There was no
difference in risk between highest and lowest UVB exposure in NHSII.
They provide a possible explanation, "The later birth cohort of NHSII
participants (born between 1946 and 1964) were more likely aware of the dangers
of sun exposure and, perhaps, had more sun-protective behavior, making
residential UVB not as good a proxy for actual sun exposure in NHSII."
They conclude that the current findings strengthen evidence that more intense
sun exposure lowers the risk of RA. “The mechanisms are not yet understood, but could be mediated by cutaneous
production of vitamin D and attenuated by use of sunscreen or sun avoidant
behavior," they explain. The authors call for further research to examine the
most effective UVB intensity and timing of exposure.
More Sunlight Linked To Fewer Strokes
As reported by Dr John Cannell (Vitamin D Council) (2/12) New Study Suggests Vitamin D Deficiency Linked To Increased Stroke Risk
Researchers at the University of Alabama announced that sunlight is inversely
associated with stroke: the more sunlight the fewer strokes. The authors also
commented on the poor wisdom of avoiding all sunlight; that is, they implied
the dermatologists have done us harm.
Strokes are the third leading cause of death in the USA, but the leading cause
of disability. High blood pressure is the single most important modifiable
medical risk factor, but inflammation (as measured by CRP) and diabetes are
major medical risk factors as well. Blacks are twice as likely as Whites to
suffer a stroke, even after scientists account for all the socioeconomic and
medical risk factors. Why do so many more Blacks die from strokes as Whites?
It is not vitamin D, according to Dr. Erin Michos and colleagues in a paper
published in the journal Nutrition. However, the researchers found that vitamin
D levels were a major risk factor for Whites but not for Blacks. Whites with
low vitamin D levels (<15 ng/ml) had a threefold higher risk for stroke compared to Whites with higher
levels. This is one of those studies where they collected blood in the late
1980s and early 1990s, froze it, and then waited to see who died of what and
when over the next 14 years.
For Whites, all the traditional risk factors were strongly influenced by 25(OH)D
levels (p= <0.0001) including, you guessed it, CRP. For Whites in the highest quartile of
vitamin D levels (mean = 44 ng/ml), they had much lower CRP (.35 vs. .48), less
diabetes (4.1 % vs. 8.9%), less hypertension (22% vs. 35%) and less cholesterol
problems (22% vs. 31%) than the Whites in the lowest quartile of vitamin D
(mean=17 ng/ml). They could not find similar robust finding for Blacks, and
they hypothesized that perhaps Blacks can get along with less vitamin D than
Whites can. That certainly does not appear to be the case in equatorial Africa.
I suspect they couldn't find the relationship here because American Blacks have
such low vitamin D levels, that the range in blood levels is not large enough
to show clinical or statistical significance. That is, so many American Blacks
are deficient and at risk of stroke, the number with vitamin D levels high
enough to help prevent stroke are negligible. As I said, the authors note
another possibility, that vitamin D metabolism is different in Blacks. Although
possible, I think it's best to treat the massive deficiency in the Black
community first. I suspect researchers will find that deficiency is deficiency,
no matter the skin color.