Killer heat waves such as the one blamed for 14,800 deaths in France in 2003 may become more common. Global warming is one part of the problem. Another part is the growing number of people who are more vulnerable to the heat because they're older and heavier, the July issue of the Harvard Health Letter explains.

Thirst declines with age, and older sweat glands don’t produce as much sweat as they used to. The sweat that is produced tends to contain more salt, and lack of salt in the body can lead to sudden drops in blood pressure.

Older people are also more likely than younger folks to be taking medications that cause fluid loss (and therefore dehydration), including some laxatives, furosemide (Lasix) to counteract water retention, and other diuretics for blood pressure control.

Besides heading for the air conditioning, staying out of the sun, and wearing loose, light clothes, the Harvard Health Letter suggests taking these steps:

• Listen to your body. Muscle cramps, fatigue, weakness, impaired concentration, confusion, lightheadedness, nausea, labored breathing, chest discomfort, and a rapid or erratic pulse can all be signs of trouble. If you feel ill — even just a little — get to a cool place, drink plenty of cool water, and seek medical help if you don’t improve promptly.
• Check up on a neighbor. Social isolation is a major risk factor for heat-related illness and death.
• Review your medications. Painkillers, for example, can reduce awareness of the heat. Talk to your doctor about your medications if temperatures are climbing, especially if you’re not protected by air conditioning.