Healthnotes Newswire (November 25, 2009)—A study recently published in the Journal of Nutrition has received widespread publicity for reporting that higher selenium levels in the blood were associated with higher cholesterol levels as well—in other words, that it may be dangerous to heart health. But don’t worry if you’ve been taking this trace mineral to protect your health: some of the study’s conclusions are questionable, and also inconsistent with previous research, some of which has suggested that selenium may actually prevent heart disease.

What they found

In the new study, researchers measured selenium levels in plasma and red blood cells of 1,042 adults participating in a diet and nutrition survey in the UK. They also measured the activity of glutathione peroxidase, an enzyme that contains selenium and which is considered to be a useful indicator of selenium nutritional status in populations with relatively low selenium intake, such as people living in the UK. The study showed:

• People with higher plasma selenium concentrations had serum cholesterol levels that were on average 8% higher than in people with lower plasma selenium concentrations.

• In contrast, there was no association between red blood cells’ selenium concentrations and serum cholesterol or between glutathione peroxidase activity and serum cholesterol.

Considering that two of the three measures of selenium status showed no association with serum cholesterol, it might be considered a stretch to conclude that higher selenium levels were associated with higher serum cholesterol. However, even granting the researchers’ conclusion, there are other explanations for their findings.

First, there were many differences between people who had high and low selenium levels

People with high selenium levels were older, ate more high-cholesterol foods, were less likely to be smokers, had higher income and educational level, and used vitamin and mineral supplements more often.

The researchers attempted to make adjustments for each of these differences, but there is no guarantee that simultaneously manipulating so many variables gives a reliable picture of the selenium-cholesterol relationship.

Second, a number of factors that influence selenium and cholesterol levels were not taken into account

For example, people who have health conditions that cause malabsorption would be expected to have both low selenium and low cholesterol levels. In addition, many people take statin drugs because they have high cholesterol. These drugs lower serum cholesterol levels and are also believed to interfere with selenium metabolism. The researchers acknowledged that they did not ask participants whether they had any health conditions or whether they were taking cholesterol-lowering drugs.

Third, if there is an association between selenium status and cholesterol levels, the association might represent effect rather than cause

People with high cholesterol levels often take multivitamin-mineral supplements as part of a program to reduce heart disease risk. In those individuals, the selenium level would be high because the cholesterol is high, not the other way around.

Justified consideration—but not conclusion

Because of these limitations, it is not possible to conclude from the new study whether selenium intake influences cholesterol levels. That information would best be obtained by giving people a selenium supplement or a placebo and seeing what happens to their serum cholesterol. Two such studies have already been done, and both found that supplementing with 100 to 300 mcg per day of selenium has no effect on cholesterol levels.

Selenium supplements have been used successfully to prevent and treat some types of heart failure, and population studies have found that higher selenium intake is associated with a lower incidence of cardiovascular disease. While these studies are not definitive, neither is there any convincing evidence that taking a modest amount of supplemental selenium (such as 50 to 200 mcg per day) increases cholesterol levels or the risk of developing heart disease.

(J Nutr 2009 Nov 11; E-pub ahead of print)