By ANAHAD O’CONNOR

THE FACTS

For migraine sufferers, summer can be a perilous time of year.

Oppressive heat and spikes in temperature have long been thought to precipitate attacks in people prone to chronic headaches. One large study in the journal Neurology even showed that the risk of migraines jumps nearly 8 percent for every nine-degree rise in temperature.

But a simple step that may lower the risk, especially in warm weather, is to stay properly hydrated. Dehydration causes blood volume to drop, researchers say, resulting in less blood and oxygen flow to the brain and dilated blood vessels. Some experts suspect that a loss of electrolytes causes nerves in the brain to produce pain signals.

Anyone who has ever woken up dehydrated after a night of heavy drinking knows this feeling as a hangover. But migraine sufferers may be more sensitive to the effects of dehydration.

In one study, also published in Neurology, scientists recruited migraine sufferers and divided them into two groups. Those in the first group were given a placebo medication to take regularly. The others were told to drink 1.5 liters of water, or about six cups, in addition to their usual daily intake. At the end of two weeks, the researchers found that those in the water group had increased their fluid intake by just four cups a day. But on average they experienced 21 fewer hours of pain during the study period than those in the placebo group, and a decrease in the intensity of their headaches.

To stay adequately hydrated, health officials recommend that men drink about 13 cups of liquid a day — from water, juice and other sources — and that women drink about 9 cups.