October 17, 1997
By Ron Brown 504 388-3867 [email protected]
BATON ROUGE -- Osteoporosis -- the loss of bone calcium -- is a problem most women face after menopause. But recent studies by LSU researchers show that swimming may be a key to keeping bones strong.
Work by human ecology professor Maren Hegsted and associate professor Michael Keenan over the past two years shows that bone-calcium loss can be minimized in post-menopausal rats that do enough exercise.
Hegsted and Keenan performed their research using retired breeder rats with an average of nine pregnancies each. "All of them had the metabolic stress of pregnancy and lactation, which was as close as we could come to mimicking an adult woman who's raised a family," Hegsted said.
Half of the rats had their ovaries removed prior to the experiment to eliminate estrogen production and simulate menopause.
"We know from past research that ovariectomized rats are just like post-menopausal women with respect to their bones. They start losing bone mineral, their bones become less dense, they lose calcium. We also know from past experience that the ovariectomized rats get fat. Their food intake increases, but they gain more weight than they should for the amount of extra food they eat," said Hegsted.
To control for the stress of the operation, the rest of the rats had similar operations, but their ovaries were left intact.
Half of both groups were used as a control, and Hegsted then put the remaining rats into a barrel of lukewarm water where they were obliged to swim. "You put the rats in for five minutes, then you take them out, dry them off and put them back in their cages and they say, ëThat was okay, it wasn't so bad.' The next day you put them in for 10 minutes. We increased their time in the water by five-minute increments until we were swimming them for 70 minutes a day, five days a week."
The results were significant. "Swimming eliminated the bone loss and weight gain due to ovariectomy. Traditionally, doctors tell women with bone loss due to osteoporosis, for instance, to do weight-bearing exercises. But there are a lot of women for whom weight-bearing exercises are very difficult -- women with conditions like arthritis or obesity. Women who cannot walk comfortably, let alone jog or run. This is a non weight-bearing exercise, but apparently it had sufficient intensity that it still had a beneficial effect on the bones.
"The question is, how much of this carries over to humans? You take a rat with a life-span of three years and you swim them 70 minutes a day. If a woman, who lives 70 years, has to do a proportional amount of exercise, it's unrealistic. We don't know in terms of quantity how it translates."
Hegsted noted, however, that the rats weren't swimming hard. They were basically just staying afloat, doing a leisurely dog-paddle. "A woman swimming laps for 30 minutes may be more than equivalent to a rat swimming for 70 minutes. To me it offers an alternative for women who can't do load-bearing exercises, or don't like to. We know it has some kind of beneficial effect."
Hegsted is presently doing dietary studies with her rats. When the results are in, she is going to combine them with her previous results and submit a proposal for funding for human studies as well as further rat studies.
"The problem is, human studies take so long to make measurable changes, because human metabolism is so slow. Human studies on the benefits of exercise have been done, but a lot of the results depend on motivation, what the control group is doing, and the intensity of the exercise being done. It's more complicated because there are so many factors involved. Rats are a lot simpler."
Hegsted said future human studies would involve collaboration with researchers at Woman's Hospital or the Pennington Biomedical Center in Baton Rouge.
"We can't prove anything till we verify it in humans." # # #
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