Investigating why heart disease generally develops later in women than men, researchers have found that the interplay between female ovarian hormones and a circadian "clock" molecule protects the heart health of women as they age.

The findings, published in the journal Cardiovascular Research, could lead to new treatment to help prevent heart disease as we grow older."This is the first study to demonstrate a link among female ovarian hormones, the circadian system which regulates the body's day-night cycle, and the observation that women enjoy significant protection against heart disease when compared to men," said Tami Martino, Professor at the University of Guelph in Ontario, Canada.

In earlier studies, Martino's team found that heart attacks were worse for males than for females of similar age. The research also uncovered a time-of-day effect: heart attacks in males were more severe during sleep.This led to the idea that the circadian mechanism - tiny clocks in all of our body's cells which regulate our 24-hour day and night processes - might work differently in male and female hearts.To test that possibility, the researchers studied old mice with a genetic "clock" mutation that desynchronises the circadian mechanism.The team discovered that female heart cells are actually different from those of males.

The males had worse cardiac glucose and energy profiles. By contrast, female hearts had a healthy cardiolipin profile and better energy.However, the advantage for females was lost when the ovaries were removed, a clear sign that hormones such as estrogen protect the heart even when the circadian mechanism is disturbed, Martino said.The findings may lead to clinical benefits for women and men, she added.