(Agencies)
Updated: 2007-12-18 15:15

Appel found 80 percent of black kidney patients in a recent study were non-dippers. Most startling, 40 percent had nighttime blood pressure that was even higher than daytime levels.

Two-thirds of chronic kidney disease patients, and at least 10 percent of the general population, are estimated to be non-dippers, says Dr. Joseph Vassalotti of the National Kidney Foundation. One theory is that their bodies have trouble excreting salt.

Yet few patients have ever heard of the problem -- and few doctors know who is affected. Most people get their blood pressure checked only during the day. A 24-hour blood pressure monitor can tell but is rarely used, partly because insurance seldom pays for the extra visit to download and diagnose the readings.

And most patients who take several once-a-day pills swallow them all in the morning, meaning they all start wearing off around the same time, says Dr. Gina Lundberg of St. Joseph's Hospital in Atlanta.

"It does make good sense to take some in the morning and some in the evening," says Lundberg, a spokeswoman for the American Heart Association.

Everyone has an internal clock, determined by genes, that affects health. Many of these biological rhythms are circadian, meaning they fluctuate on a 24-hour cycle.

Consider how that can affect the timing of treatments. Some older "statin" pills fight cholesterol best if taken at bedtime; they target a liver enzyme that's most active at night. Asthma attacks are more frequent at night, and the stomach secretes more heartburn-causing acid at night, affecting some patients' dosing requirements. Researchers even are studying how to better time certain cancer chemotherapies and allergy treatments.

The best-known example: Blood pressure jumps in the early morning hours, as the awakening body produces more stress hormones. That's also why heart attacks and strokes are most common in the morning.

The nighttime dipping problem has gotten far less attention. The new Italian study marks an important advance, says Dr. Mahboob Rahman of the University Hospitals of Cleveland.

"We know now that you can change medication timing and lower blood pressure at night," he explains.

That doesn't mean everyone should switch willy-nilly to bedtime dosing. Morning may be best for people on just one drug, and no one yet knows if the switch truly gives non-dippers better overall health. "That's the million-dollar question," Rahman cautions.

Still, Lundberg says it's worth asking your doctor how to time doses, saying one at night for someone taking multiple medicines couldn't hurt.

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