Flu shot works better in women than in men

The new research suggests that more of the hormone testosterone causes men to have a weaker immune response to the flu vaccine than women, Fox News reports.

Researchers, led by Mark Davis of Stanford University, measured immune responses in 53 women and 34 men after a seasonal flu shot. The women's bodies produced more flu antibodies and cytokines, as expected.

Next, the researchers tested the subjects' blood serum responses to different influenza strains. They found the biggest difference between the sexes' infection-fighting abilities appeared when their blood was exposed to H3N2, a particularly virulent flu strain.

Finally, they identified two genes known to be associated with both poor immune response and metabolizing fat in the blood. The scientists found that these genes are regulated by testosterone. The higher the body's testosterone level, the weaker its immune response.

This new data may help explain why women are at greater risk for autoimmune diseases, such as multiple sclerosis and lupus.

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