The way weather affects your health; believe it or not, high humidity can aggravate arthritis, and a warm wind may bring on a migraine. Here's how the weather can influence you physically and mentally - Our Planet and Your Health

SINCE 400 B.C., PEOPLE HAVE blamed the weather for all types of ailments. And they still do. Log on to the Weather Channel's website and you'll find an "Aches and Pains" forecast for your area. (It may tell you to expect a flare-up in knee pain, for example.) Across the Atlantic, the British Meteorological Office in England reports weather conditions to doctors so they can prepare for an increase in asthma attacks. And in Germany, television stations dispense daily weather-related health reports.

But are these health forecasts based on anything more than old wives' tales? Yes, they are. Though preliminary, scientific studies back up the notion that weather affects your health, says Esmaiel Malek, Ph.D., a biometeorology professor at Utah State University in Logan. Read on--you may be surprised by what scientists have discovered about the weather and your health. Keep in mind that you shouldn't move across the country in search of better weather just yet. But you may understand why you feel the way you do on certain days.

Temperature's Toll

Hundreds of studies link temperature, humidity, air pressure, or wind to arthritis, asthma, migraines, and other ailments. But most experts say the strongest evidence exists for the effect of temperature on your health.

When temperatures rise, heart, vascular, and respiratory problems increase, says Scott Sheridan, Ph.D., a climatology professor at Kent State University in Kent, Ohio. High temperatures force your blood vessels to constrict and your blood pressure to increase so you can release excess heat through your skin, according to Larry Kalkstein, Ph.D., a professor at the University of Delaware's Center for Climatic Research in Newark. But if you can't cool yourself sufficiently in this way, your body overheats. This exacerbates any cardiovascular problems and may cause heat stress.

In warmer weather, respiratory troubles may result from poor air quality. Scientists know that on hot, sunny days, compounds from car exhausts and industrial pollution interact with sunlight to form ozone. Ozone can inflame your airways and reduce lung function, says Susan Stone, an environmental health scientist for the Environmental Protection Agency in Research Triangle Park, N.C. In a study published in the Lancet early this year, researchers observed 3,535 healthy children for five years. They found that kids playing sports outside when ozone levels were high had a higher risk of asthma.

Yet respiratory problems Can also occur with cold temperatures. Sheridan says research shows that children are five times as likely to have an asthma attack during the first cold spell in the fall than in the spring or summer. Cold air traps pollutants like factory smoke close to the ground. The irritants may diminish your lung function, leaving you vulnerable to asthma and indoor allergens. Poorly cleaned heating systems also contribute to asthma and allergy attacks in the fall and winter, say researchers.

A chill in the air may cause muscle aches and joint pains as well. A February 2002 study in the Journal of Rheumatology followed 151 patients in Cordoba, Argentina, with osteoarthritis, rheumatoid arthritis, or fibromyalgia for one year. All three groups of patients experienced increased pain on cooler days. This study also found that humidity and air pressure triggered pain.

Humidity's Sticky Situations

Just like temperature, humidity plays a key role in your well-being. In the Argentine study, the researchers concluded that high humidity contributed to flare-ups of both osteoarthritis and rheumatoid arthritis. (Humidity was not linked to fibromyalgia.) Researchers aren't sure why humidity appears to increase aches. However, they do know why hot, humid days can cause fatigue. Normally, your body perspires to cool you down when temperatures are high, according to Malek. But if the humidity is also high, you're trapped in a moist environment where your sweat can't evaporate and escape from your skin. This causes you to expend extra energy, which can leave you feeling sluggish or fatigued.

Air Pressure's Highs and Lows

Many experts consider air pressure--especially changes in air pressure--to be a major factor in how weather affects you. For example, high-pressure systems that occur on hot summer days or on high-ozone days in the fall or winter may lower your ability to concentrate, says Klaus Bucher, Ph.D., a biometeorology researcher and meteorologist for the German weather service in Freiburg, Germany. In addition, he notes that German researchers tested people by having them complete tasks requiring concentration or quick reactions and found that a change in air pressure lowered their ability to concentrate.

Anecdotal evidence shows that low-pressure systems increase arthritis aches and migraines in some people, according to Malek. Although preliminary studies suggest this, more comprehensive research is necessary. Research does show that low air pressure may increase the risk of more severe problems, according to a review study published in a Slovakian journal in 1999. Researchers compared incidences of strokes in eight Slovakian health institutions in Bratislava against weather patterns for two years, and determined that low pressure was connected to higher rates of stroke. Interestingly, new research presented at the American Academy of Neurology's annual meeting last April shows that high air pressure may also contribute to increases in strokes. Further study is needed.