May 23, 2000 -- People taking vitamin C to cancel out the health consequences of smoking should take note. Although some previous studies have shown that injections of vitamin C can improve smoking-related damage of the blood vessels, a new study in the May issue of the Journal of the American College of Cardiology suggests that extra vitamin C has no real benefits for smokers.
Because smoking is known to cause damage to blood vessels that can lead to heart disease and stroke, scientists have looked for ways to prevent that damage, or possibly reverse it. Research has shown that levels of vitamin C are generally lower than normal in the blood of smokers. Vitamin C, like many other vitamins, is an antioxidant, and may have beneficial effects on the heart and other organs.
It has been suggested that boosting the blood levels of vitamin C might improve function in blood vessels that have been damaged by years of smoking. Indeed, some studies have shown that injections of high doses of vitamin C can reduce the damage to some extent but have shown no evidence that long-term damage to the blood vessels can actually be reversed. Researchers who conducted those studies always questioned whether the good results seen with the vitamin C injections could be gained by taking vitamin C tablets.
The new study seems to validate those concerns. In addition, whatever benefits vitamin C may initially have do not persist over time, writes lead author Olli Raitakari, MD, PhD, of the Royal Prince Alfred Hospital in Sydney.
The study of eight male and 12 female smokers with an average age of 36 found that a single high dose of vitamin C taken by mouth significantly increased the amount of vitamin C in the bloodstream and improved blood flow in a main blood vessel in the upper arm. But Raitakari and colleagues found that daily ingestion of the vitamin at half that dose for eight weeks resulted in no significant or sustained benefit, even though levels of the vitamin remained high in the bloodstream.
How smoking causes damage to the arteries is unclear. What is known is that smoking increases the amount of "free radicals" in the blood, which occur naturally in everyone but are highly destructive. Free radicals can change or damage the lining of the walls of blood vessels. Antioxidant vitamins such as vitamin C and vitamin E are thought to help out by "mopping up" the free radicals in the blood and limiting the amount of damage they can cause. But smoking causes many other changes as well, making it hard for researchers to pinpoint a single reason behind smoking's harmful effects.
One expert who reviewed the study said smokers should not jump to the conclusion that taking vitamin C daily is of no use to them.
Balz Frei, PhD, director of the Linus Pauling Institute in Corvallis, Ore., says vitamin C has many beneficial effects beyond heart disease prevention that make it a wise choice as a daily supplement for people who smoke. He says smokers use up vitamin C at a higher rate than nonsmokers and therefore need about 35 mg more of the vitamin per day than those who do not smoke.
Frei's group published a study last year showing that daily supplements of vitamin C for one month led to improvements in blood vessels that had been damaged by smoking. He says the new study is at odds with the majority of other studies on the subject.
"I think there is a real effect, although there may be some exceptions. The overall evidence is very compelling," he tells WebMD.
- Contrary to previous findings, a new study shows that vitamin C does not protect the blood vessels from damage caused by smoking.
- It is unclear exactly how smoking causes damage to the blood vessels, but it does increase the formation of free radicals in the blood, which occur in everyone but are very damaging.
- Smokers have lower levels of vitamin C in their blood than nonsmokers, because they use it up at a faster rate, so taking a vitamin C supplement may be a good idea for its other beneficial effects, according to one expert.