Harsh weather could nudge up your weight, new research shows.

It might not take a tornado, blizzard, or even a thunderstorm to make a difference. Hot and cold temperatures could also have an effect, say Baylor University's Ge Lin, PhD, and colleagues.

The problem, they suggest, is that when it's too hot or too cold outside, people may avoid physical activity. That might sound like common sense, and their research seems to support that idea.

With summer coming, it might be a good time to plan ahead for hot months. Options include shifting activities to cooler parts of the day or working out in a gym. Drinking enough water, dressing appropriately, and protecting skin from the sun are also important.

Ideal Conditions

Outdoor temperatures from 25-85 degrees Fahrenheit are considered amenable to physical activity, say Lin and colleagues. They did an extensive literature review to come up with that range.

Hourly U.S. weather records from 1990 to 1995 showed how often those ideal weather conditions occurred. Data on physical activity and body mass index (BMI) came from the 2002 Behavioral Risk Factor Surveillance System, a national phone survey done by the CDC in all U.S. states, territories, and Washington, D.C.

Weather and Weight

Physical activity and BMI suffered in areas with inhospitable climates, say Lin and colleagues. They even took individual risk factors, county road density, and median household income into account.

"We concluded that the contribution of less amenable climate to overweight and obesity at the population level cannot be ignored," say the researchers. They presented their findings in Washington, D.C., at the American Heart Association's 45th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.

The researchers say that "given the unmodifiable nature of outdoor climate, we recommend that various environmental interventions be devised to mitigate its negative effect [on health]."

Here are some ways to help minimize the risk of heat illness, which may help individuals continue routine exercise despite poor weather conditions:

— Wear light-colored, loose-fitting clothing while exercising.

— Take frequent breaks in the shade.

— Know the warning signs of dehydration and heat exhaustion. They include dry lips and tongue, headache, weakness, dizziness or exhaustion, nausea, and muscle cramping.

During cold weather conditions consider:

— Layering clothing for outdoor activities

— Exercising indoors, for example at an indoor track, gym, or mall

— Using exercise equipment at home

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: American Heart Association's 45th Annual Conference on Cardiovascular Disease Epidemiology and Prevention, Washington, D.C., April 29-May 2, 2005. News release, American Heart Association. WebMD Feature: "Heat Can Beat the Best Athlete."