January 8, 2014
High Testosterone in Men Dampens Flu Vaccine Effectiveness

Stanford, CA—Higher testosterone levels may confer some health benefits to men, but robust response to the influenza vaccine isn’t one of them.

That’s according to research at the Stanford University School of Medicine, which has linked high testosterone levels in men to a poor immune response to the influenza vaccine. The study was published online recently in the Proceedings of the National Academy of Sciences.

According to the report, measurement of the boost in protective antibodies after influenza vaccination indicates that those with relatively high amounts of circulating testosterone actually benefit less.

Researchers found that women had a generally stronger antibody response to the vaccine than men and that the response from men with relatively low testosterone levels was similar to females.

“This is the first study to show an explicit correlation between testosterone levels, gene expression and immune responsiveness in humans,” said the study's senior author, Mark Davis, PhD, professor of microbiology and immunology and director of Stanford's Institute for Immunity, Transplantation and Infection. “It could be food for thought to all the testosterone-supplement takers out there.”

Background in the article points out that past research has shown that men are more susceptible to bacterial, viral, fungal and parasitic infection and that their immune systems don't respond as strongly as women's to vaccinations against influenza, yellow fever, measles, hepatitis and many other diseases.

Researchers have suggested that could be related to women’s higher average blood levels of signaling proteins that help create inflammation to activate the immune system. Testosterone, however, has been shown to have anti-inflammatory properties, signaling a possible interaction between the male sex hormone and immune response.

Ongoing longitudinal research at Stanford was used for the investigation. Since 2008, participants at a range of ages have been getting blood drawn before and after receiving annual influenza vaccines. Their blood samples are analyzed for tens of thousands of variables, including circulating levels of numerous immune-signaling proteins; counts of various blood-cell subtypes; and the degree to which circulating immune cells are active or inactive, according to the authors.

In analyzing samples from 53 women and 34 men, the research indicates that, on average, the women had significantly stronger antibody responses to the influenza vaccine. While the women also showed higher average prevaccination blood levels of proinflammatory immune-signaling proteins, prevaccination levels of those proteins in a particular woman's blood didn't significantly predict the degree of her postvaccination antibody response.

“Most studies don't report on sex differences, a major determinant of variation in immune response,” noted the study's lead author, David Furman, PhD, a Stanford research associate.

When the 34 men were divided into two groups—those with circulating levels of testosterone in its bioactive form above the median level and those with below-median levels of the hormone—high-testosterone and high-activation levels of Module 52 genes were linked to reduced postvaccination antibody levels.

Davis pointed out that the lessened response isn’t all bad. Women are twice as susceptible to sepsis as men, suggesting that having a somewhat weakened immune system could be more life-saving than life-threatening for a dominant male in the prime of life, he explained.

U.S. Pharmacist Social Connect