SAN DIEGO -- Vitamin C pills may speed up hardening of the arteries, researchers suggest in a new study they called a disturbing surprise.
The researchers cautioned that more experiments are needed to know for sure whether megadoses of the vitamin actually are harmful.
Still, they said the finding supports the recommendations of health organizations, which generally urge people to avoid high doses of supplements and to get their nutrients from food instead.
Many people load up on vitamin C and other nutrients on the assumption that these supplements are good for their health, even though there is little scientific evidence this is true. In theory, vitamin C and some other nutrients might protect the circulatory system and other organs by suppressing the damaging effects of oxygen.
''When you extract one component of food and give it at very high levels, you just don't know what you are doing to the system, and it may be adverse,'' said Dr. James Dwyer, an epidemiologist who directed the study. He presented the findings Thursday at a meeting in San Diego of the American Heart Association.
Clogged arteries -- what doctors call atherosclerosis -- are the major underlying cause of heart attacks and strokes.
In the latest study, doctors looked for early signs of this process by twice performing ultrasound scans on volunteers' carotid arteries, once at the study's start and again 18 months later.
Dwyer and colleagues from the University of Southern California studied 573 outwardly healthy middle-aged men and women who work for an electric utility in Los Angeles. About 30 percent of them regularly took various vitamins.
The study found no clear-cut sign that getting lots of vitamin C from food or a daily multivitamin does any harm. But those taking vitamin C pills had accelerated thickening of the walls of the big arteries in their necks. In fact, the more they took, the faster the buildup.
People taking 500 milligrams of vitamin C daily for at least a year had a 2 1/2 times greater rate of thickening than did those who avoided supplements. Among smokers, the rate was five times greater.
''If a person's physician has prescribed vitamin C, it is appropriate to be taking it,'' Dwyer said. ''But if you are a healthy person and taking them in hopes of preventing cardiovascular disease, the heart association does not recommend it. This study would suggest that recommendation is prudent.''
Another study released at the meeting Thursday documents for the first time that smoking pot increases the risk of a heart attack.
The chance of keeling over from a single joint is tiny, just as no one dies from one cigarette. But the cumulative effect on large numbers of 1960s children taking their pot habit into middle age could be significant.
''With baby boomers aging, more people in (their) 40s and 50s are smoking marijuana than in prior generations,'' said Dr. Murray Mittleman of the Harvard School of Public Health and Boston's Beth Israel Deaconess Medical Center. ''The risk of coronary artery disease increases with age. Whether this will emerge as a public health problem remains to be seen.''
The study found that the risk of a heart attack is five times higher than usual in the hour after smoking a joint.
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