Daily consumption of four cups of coffee may give you the jitters, but a Johns Hopkins study has concluded that it can't be blamed for raising levels of blood cholesterol to any harmful degree.
The good news for coffee enthusiasts emerged from a study of 100 healthy men -- coffee drinkers all -- who volunteered for a study aimed at testing long-held suspicions that even moderate consumption can increase a person's risk of developing heart disease.
Researchers at the Johns Hopkins School of Medicine wanted to see if coffee heightened one of the primary causes of heart disease: high levels of cholesterol in the blood, a condition that is thought to predispose some people to clogged coronary arteries.
The 16-week study, described in today's Journal of the American Medical Association, found that the link was weak: a four-cup-a-day regimen of filtered coffee raised a person's cholesterol only slightly. And the difference wasn't enough to put the heart in any danger.
Although the study may put one concern to rest, the larger mystery of coffee's effects on human health has not been settled.
"It's still an open question," Dr. David M. Levine, director of internal medicine at the Johns Hopkins School of Medicine, said at a news briefing yesterday. "The current study shows that if there turns out to be a positive relationship [between coffee and heart disease], it's not due to cholesterol."
Another Johns Hopkins study has found preliminary evidence that coffee drinkers have slightly higher rates of heart disease, but that study was not designed to rule out the possibility that other factors such as smoking or fatty diets were actually to blame. And to further confuse the issue, a well-known study based in Framingham, Mass., has found no link between coffee and heart disease.
In the cholesterol study, four-cup-a-day drinkers saw their cholesterol increase from an average level of 200 milliliters per deciliter of blood to 209 milliliters, but one-third of the difference was a boost in the so-called "good cholesterol" -- the high-density lipoproteins that are thought to protect people from heart disease.
"That was a real surprise for us," said Dr. Roy Fried, the study's principal investigator, who recently left Hopkins to work for Kaiser Permanente medical group in Kensington. "Nobody has noted a rise in HDL before."
Two-thirds of the increase was "bad cholesterol," low-density lipoproteins, but Dr. Fried said the "good cholesterol" fully compensated for the bad.
Filtering the coffee may remove unknown substances that are capable of raising blood cholesterol, Dr. Fried said. That possibility exists because a Scandinavian study found a link between boiled coffee and high cholesterol.
If there is a mystery substance, Dr. Fried said, it's not caffeine because the chemical passes right through the filter paper. The Hopkins researchers decided to test filtered coffee because it is the most popular method of coffee-making in America.
The study was funded by a $300,000 grant from the National Coffee Association, a trade group that was interested in resolving conflicting evidence about coffee's health effects. Although he acknowledged that the group's purpose is to promote coffee, Dr. Fried said the association did not interfere in the study's design and execution.
In the study, the volunteers were first asked to abstain for coffee for a "cleansing period" of eight weeks. Then, they were randomly assigned to four groups.
One drank four cups of caffeinated coffee a day; one drank two cups of caffeinated coffee; another drank four cups of caffeine-free coffee; and a fourth drank no coffee.
Only the people drinking four cups of caffeinated coffee experienced a rise in their cholesterol levels.