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Selenium Reduces CVD and All-Cause Mortality

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I don't usually post about the benefits of getting the RDA of specific micronutrients. It should be a no-brainer by now that people should run their diet through nutrition tracking software like CRON-O-Meter to make sure they aren't deficient in essential micronutrients. But this large new cohort study [1], posted by Al Pater to the email list (thanks Al!), found such a big benefit from higher intake of selenium (Se) that I thought it worth posting about.


In [1], the researchers followed 133,000+ adult (40-75 years old) men and women for an average 8-13 years, during which time about 10,000 of them died. They looked at their likelihood of dying from CVD, cancer and all-causes based on what quintile of selenium intake they were in. What they found was pretty striking. While (surprisingly - given previous results) Se intake didn't make any difference for cancer mortality, for both CVD and all-cause mortality there was a strong inverse association between Se intake and mortality. In particular men and women in the highest quintile of Se intake were about 20% less likely to die of any cause, and men were 33% less likely to die of CVD, even after statistical adjustment for all the usual potential confounders.


How much Se was the highest quintile consuming? The average intake of men in the highest quintile was 70 mcg/day, a bit higher than the US RDA of 55 mcg/day, compared with about 27 mcg/day in the lowest quintile, which is about 1/2 the US RDA. The mortality results displayed a dose-response relationship across the quintiles, making the trend quite significant (p for trend = 0.0001):


The corresponding HR among men were 1·00 (reference), 0·91 (95 % CI 0·83, 0·99), 0·86 (95 % CI 0·78, 0·95), 0·82 (95 % CI 0·73, 0·91) and 0·79 (95 % CI 0·70, 0·89), respectively (P=0·0001 for trend across categories).


The discussion section is quite interesting and important. In it, the authors put their results into the context of previous studies involving selenium. They cite several prospective cohort studies which found similar results, namely higher baseline selenium intake or plasma levels were associated with lower mortality. But interestingly, they say several intervention trials have not observed mortality benefits from selenium supplements, either alone or in combination with other supplemental micronutrients:
Although a meta-analysis of observational studies showed a
significant inverse association between Se concentration and
risk of CHD (ref), randomized trials using Se in combination with other
antioxidants have not shown a significant protective effect
on CVD or mortality (ref, ref). However, most of these large
prevention trials did not consider baseline nutrition level
in their inclusion criteria and Se was given in combination
with other vitamins and minerals in all but two trials (ref,ref).
In short, the authors are suggesting that too much selenium (i.e. too much above the RDA), or selenium in supplement form or in combination with other supplemental micronutrients, might not be so good - hence the discrepancy between their results and intervention trials.
This seems to suggest it may be important to get one's RDA of selenium, but not too much more. So don't go overboard on those brazil nuts - half of one nut per day should be sufficient, or if you'd rather not play roulette with your selenium intake, you might consider a supplement rather than a fraction of a brazil nut. 
[1] Public Health Nutr. 2016 May 20:1-8. [Epub ahead of print]
Dietary selenium intake and mortality in two population-based cohort studies
of 133 957 Chinese men and women.
Sun JW, Shu XO, Li HL, Zhang W, Gao J, Zhao LG, Zheng W, Xiang YB.
To investigate the potential influence of dietary Se intake on mortality
among Chinese populations.
We prospectively evaluated all-cause, CVD and cancer mortality risks
associated with dietary Se intake in participants of the Shanghai Women's
Health Study (SWHS) and the Shanghai Men's Health study (SMHS). Dietary Se
intake was assessed by validated FFQ during in-person interviews. Cox
proportional hazards models were used to calculate hazard ratios (HR) and 95
% CI.
Urban city in China.
Chinese adults (n 133 957).
During an average follow-up of 13.90 years in the SWHS and 8.37 years in the
SMHS, 5749 women and 4217 men died. The mean estimated dietary Se intake was
45.48 ?g/d for women and 51.34 ?g/d for men, respectively. Dietary Se intake
was inversely associated with all-cause mortality and CVD mortality in both
women and men, with respective HR for the highest compared with the lowest
quintile being 0.79 (95 % CI 0.71, 0.88; P trend<0.0001) and 0.80 (95 % CI
0.66, 0.98; P trend=0.0268) for women, and 0.79 (95 % CI 0.70, 0.89; P
trend=0.0001) and 0.66 (95 % CI 0.54, 0.82; P trend=0.0002) for men. No
significant associations were observed for cancer mortality in both women
and men. Results were similar in subgroup and sensitivity analyses.
Dietary Se intake was inversely associated with all-cause and cardiovascular
mortality in both sexes, but not cancer mortality.
China; Dietary; Mortality; Prospective study; Selenium intake
PMID: 27197889
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