Here's a new study finding that's bound to make tall, thin women happy: Their body size and their gender make it more likely they will reach the milestone age of 90 than either men or shorter, heavier women.

If these women exercised an hour a day, the longevity benefits were even greater, the Dutch scientists reported. While exercise helped men live longer, their body size did not.

The increase in life expectancy has started to plateau in some developed countries, said lead researcher Lloyd Brandts, from the department of epidemiology at Maastricht University Medical Centre, in the Netherlands.

One theory that might explain this is the growing number of obese and sedentary people, he said. But the new study unearthed a surprise.

"The findings indicate that both body size and physical activity are related to lifespan, but that these associations seem to differ between men and women," Brandts said.

He cautioned, however, that this type of observational study can't prove body size and physical activity cause people to live longer.

Brandts said that, in women, an increasing chance of reaching 90 was seen with up to 60 minutes of physical activity a day. Chances of reaching old age did not increase further with more exercise.

But, "in men, it seems the more time they spend physically active every day, the better it is for their chances of reaching old age," he added.

In the study of over 7,800 men and women, the Dutch researchers also found that taller women who were thin at the start of the study and remained thin were more likely to make it to 90 than shorter, heavier women.

Women who were about 5 feet 9 inches tall were 31 percent more likely to reach 90 than women who were around 5 feet 3 inches tall, the findings showed.

Among men, however, height didn't provide a similar advantage, the researchers found.

In terms of being physically active, men who exercised more than 90 minutes a day were 39 percent more likely to reach 90 than men who were physically active for less than 30 minutes.

Every extra 30 minutes of daily physical activity was linked with a 5 percent increase in the odds of turning 90, the investigators found.

For women, however, those who were physically active for 30 to 60 minutes a day were 21 percent more likely to reach 90, according to the report.

For the study, Brandts and colleagues collected data on just over 7,800 men and women, aged 55 to 69, who took part in the Netherlands Cohort Study, which began in 1986.

The participants gave information on their weight and height when they were 20. They also described their leisure time physical activity.

Activities included gardening, dog walking, working around the house, walking or cycling to work, and sports.

Participants were monitored until they died or they turned 90. Behavior and a history of illness also seemed to play a role in lifespan, as did smoking, the study authors said.

Dr. David Katz, director of the Yale University Yale-Griffin Prevention Research Center, said, "Since most adults, both men and women, get less than an hour of physical activity daily, the takeaway message for now is more physical activity is better for both sexes."

As to why height and weight affect lifespan for women, the answers are only speculative, Katz said. The benefit of being lean appears to be the common factor among both men and women, he added.

And it may be a problem of stigma and depression, he said.

"Women consistently suffer the effects of obesity bias more than men, so the mental health costs may be greater," Katz suggested.

Because excess weight in men is less stigmatized, it may be that men with perfectly good mental health tend to gain weight over time, he said. Women, however, may be more reluctant to gain weight, and gaining weight may be indicative of poor mental health or other sources of duress, Katz noted.

The study was published online Jan. 21 in the Journal of Epidemiology and Community Health.