NEW YORK (Reuters Health) - In a new study from a single California community, women who had been pregnant at least four times were less likely to die from cardiovascular disease than those whod never been expecting. Researchers said that could be due to the protective effects of pregnancy-related hormones as well as the extra social support that comes with having more children or the fact that women who are able to get pregnant more often are healthier to begin with. Its not clear that getting pregnant more often protects womens hearts, necessarily. Its just one more little piece of the puzzle that maybe physicians should be aware of or think about, said Donna Kritz-Silverstein, from the University of California, San Diego. Heart disease is one of the biggest problems facing women today. Its the leading cause of death among women in the United States, Kritz-Silverstein, who worked on the study, told Reuters Health. But, she added, Many women dont perceive themselves to be at risk. According to the Centers for Disease Control and Prevention, heart disease kills more than 600,000 Americans a year, about half of them women. The new study, led by Marni Jacobs at UCSD, involved close to 1,300 women from Rancho Bernardo in Southern California. In the mid-1980s, when participants were in their early 70s, on average, researchers asked them how many times they had been pregnant and given birth. They also surveyed women about lifestyle habits related to heart health, such as smoking and exercise, and measured their cholesterol, blood pressure, height and weight.