Mercury in Seafood Not a Risk Factor for CVD Death

Exposure to mercury in seafood does not appear to raise the risk for death from cardiovascular disease (CVD) or any cause, according to US National Health and Nutrition Examination Survey (NHANES) data.

“Our study showed that the environmental mercury exposure at the currently low-to-moderate level was not associated with risk of all-cause or CVD mortality among US adults,” Yangbo Sun, MD, PhD, Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, told | Medscape Cardiology.

“At the current mercury exposure levels in US adults, this study does not provide evidence to change the current dietary guidelines recommending seafood consumption as part of a healthy diet for US adults, in terms of concerns about the cardiovascular effects of mercury,” Sun said.

“However, these findings are not relevant to the dietary guidelines for specific subpopulations such as pregnant women, where attention to the neurotoxic effects to their children of methylmercury exposure from specific fish species is important,” Sun said.

The study was published online November 29 in JAMA Network Open.  

Fears of Mercury in Seafood Unjust?

Seafood is packed with heart-healthy omega-3 fatty acids. But many people limit their seafood intake over fears of mercury exposure from seafood, making it important to clarify the potential health effects of current mercury exposure in contemporary populations, the researchers say.

To that end, they evaluated trends in blood mercury concentrations and the association of seafood consumption and blood mercury concentrations with all-cause and CVD-related mortality in a nationally representative sample of 17,294 adults who participated in NHANES from 2003-2012.

Seafood consumption was assessed via two 24-hour dietary recalls and mercury exposure was assessed by blood mercury levels.

Participants had a mean age of 45.9 years, 53.3% were women and the mean blood mercury concentration was 1.62 μg/L. During 131,276 person-years of follow-up, 1076 people died, 181 of these from CVD.

In multivariable analysis, an increase in seafood consumption of 1 oz equivalent per day was not associated with risk for all-cause mortality (adjusted hazard ratio [HR], 0.84; 95% CI, 0.66 – 1.07) or CVD-related mortality (adjusted HR, 0.89; 95% CI, 0.54 – 1.47).

Additionally, blood mercury levels were not associated with the risk for all-cause or CVD-related mortality.

When comparing the highest with the lowest quartile of blood mercury level, the multivariable-adjusted HRs were 0.82 (95% CI, 0.66 – 1.05) for all-cause mortality and 0.90 (95% CI, 0.53 – 1.52) for CVD-related mortality.

The lack of association between blood mercury concentrations and mortality was independent of dietary intake of EPA and DHA or selenium.

Caveats and Cautionary Notes

Strengths of the study include the nationally representative sample of US adults and the detailed and high-quality data collection in the NHANES, allowing for the control of potential confounding effects from a variety of demographic, socioeconomic, dietary, and lifestyle factors; health status; and family history of CVD, the authors note.

A limitation of the study is that only one measure of blood mercury concentration was available; thus, it may not indicate long-term exposure, which may have contributed to the null association, they point out.  

The small number of deaths from CVD is another limitation, which may have limited the statistical power to detect a significant association. Also, despite adjustment for a variety of potential confounders, residual confounding may still exist.

Despite these and other limitations, the findings “do not support an association of usual levels of concentrations to environmental mercury with mortality among US adults,” the researchers write.

As such, the findings “may inform future public health guidelines regarding mercury exposure, seafood consumption, and cardiovascular health promotion,” they say.

The study was partly supported by a research grant from the National Institutes of Health. The authors have disclosed no relevant financial relationships.

JAMA Netw Open. Published November 29, 2021. Full text

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