Postmenopausal women who take statins to manage their cholesterol levels may be more likely to experience an increase in aggression over time than those who don't take statins, a new study suggests.

In the study, researchers looked data from a previous study in which about 1,000 people were randomly assigned to take either statins or a placebo for six months. They found that among women older than 45, those who took statins showed an increase in aggressive behavior over the course of the study, compared with those who took the placebo.

But in men who took statins, aggressive behavior decreased over time, on average, compared with those who took a placebo. The men in the study were ages 20 and older, whereas the women were older, and were all post-menopausal.

"The data reprise the finding that statins don't affect all people equally — effects differ in men versus women, and younger versus older," study author Dr. Beatrice A. Golomb, a professor of medicine at the University of California, San Diego School of Medicine, said in a statement. "Female sex and older age have predicted less favorable effects of statins on a number of other outcomes as well, including survival."

The people in the study took one of the two types of statins: simvastatin (sold as Zocor) or pravastatin (sold as Pravachol or Selektine). Neither the people in the study nor the researchers knew which participants were receiving which drugs, or whether they were getting the placebo.

The researchers measured the people's levels of aggression at the beginning and the end of the study by asking whether they had engaged in any aggressive acts against others, themselves or other objects in the prior week. [7 Bizarre Drug Side Effects]

There were some exceptions in terms of aggression levels in the men in the study: Three of the men in the study who took statins experienced very large increases in aggression over time. Two of these men, with the biggest increases in aggression, were on simvastatin, which had previously been shown to affect sleep.

In fact, both of these men also developed significant sleep problems while taking the medication, and this likely contributed to the rise in aggressive behavior, the researchers said. "The degree to which your sleep problems worsened on statin," were linked with the increase in aggression, Golomb said.

Previous research has also shown that simvastatin can lower men's levels of testosterone. In the new study, the researchers confirmed that link, and also found that the degree to which testosterone dropped in men as a result of using the drug predicted the degree of their reduction in aggression, Golomb said.

But sleep and testosterone levels are not the only factors that may explain exactly why statins appear to affect people's levels of aggression. These opposite effects of statins on aggression have also been shown in studies examining people's risk of physical health conditions such as cancer, the researchers noted.

"The underlying reason is likely that statins have both pro-oxidant and antioxidant effects," and therefore the net effect of the drugs on a person's body chemistry may vary from person to person, Golomb told Live Science.

The new study was published today (July 1) in the journal PLOS ONE.

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