Women whose mothers lived to 90 years have a 25 percent greater chance to also live that long compared with those whose mothers didn't, said University of California, San Diego researchers.

Moreover, the women achieved this extreme longevity while staying healthy. They had no major chronic diseases, such as heart disease, diabetes, cancer, hip fracture or physical limitations.

When both parents survived to 90 years, the advantage jumped to 38 percent, said the study, published in the journal Age and Ageing.

If only the father lived to be 90, there was no increase in healthy longevity for the daughter. These results are probably a combination of genetics, environment and behavior, said UCSD's Aladdin Shadyab.

The study examined the health records of a racially and ethnically diverse population of more than 20,000 women and used information from the Women's Health Initiative, a large, long-term study on major risk factors for chronic diseases. The initiative has yielded a wealth of information about women's health, including the effects of hormone therapy, diet and calcium and vitamin D.

A lot of factors go into total life expectancy. This effect of long-lived parents adds an additional calculation. For a baseline comparison, 34 percent of American women 65 years old will live to 90, the Social Security Administration said. The increase in life expectancy is calculated compared to this base. (Just 22 percent of men of that age will reach 90). In addition, total life expectancy has grown over the decades. In 1965, just 25 percent of 65-year-old U.S. women lived to 90, and only 10 percent of the men.

In addition to outside factors such as exercise and diet, researchers in recent years have found some genetic traits that appear more commonly in those who achieve very long life spans. "There are specific genes that predict your ability to live longer, which these women likely inherited from their parents," Shadyab said. Researchers don't know, however, why the mother's longevity seems to play a more important role in a daughter's life span than the father's. "Further, the women whose parents lived longer had higher socioeconomic status, meaning that they were more educated with higher income."

It's possible that the parents who lived to 90 also practiced good health habits that they passed along to their daughters.

If women want to know how the results apply to them, their present age makes a difference. Older people have a better chance of great longevity than younger people. That's because some younger people will die prematurely, whether by illness or injury, and never reach old age. By definition, the elderly have survived these dangers.

For young women, this means that environmental and behavioral patterns are much more important to attaining extreme longevity than for those who are already older.