Free Radical Effects - Stroke

Stroke is the devastating consequence of a loss of the blood supply to a part of the brain so that damage occurs and the affected person is deprived, often permanently, of the full use of one or more of the brain functions movement, sensation, speech, comprehension, vision, and so on. Threatened strokes are called transient ischaemic attacks (TIAs). These are mini strokes lasting for less than 24 hours and then, apparently, reversing. Any of the manifestations of a full stroke may occur and TIAs are clear indications that one is at risk.

On 27 June 1992, the Lancet carried a paper from the Department of Neurology at Brussels University. This paper describes a study of 80 people who were showing definite signs of being at severe risk of developing a stroke. In this study, patients with TIAs lasting for more than three hours were matched against similar people who had never had TIAs, and the outcome assessed after 21 days. It was found that people with more than average vitamin A in their blood were significantly more likely to make a complete recovery than those with average amounts or less.

The trial also showed that those people whose symptoms and signs persisted for more than 24 hours, and whose blood levels of vitamin A were higher than average, ended up with less neurological damage than did those with low blood concentrations of the vitamin. Levels of vitamin E were assessed but no significant difference was found between those with below or above average concentrations of this vitamin.

Destructive of nerve cells in stroke and pre-stroke conditions is known to be partly due to oxidative damage by free radicals. The body does what it can to protect against these free radicals, but its capacity to do so is limited. Since you now know that vitamin E is highly effective in mopping up free radicals you may be wondering why it showed no useful effect in this case. Vitamin E works well in the presence of high concentrations of oxygen but not when there is a shortage of oxygen. Strokes and TIAs occur because not enough oxygen is reaching the nerve cells. Nerve cells in the brain have a higher rate of oxygen usage than any other cells in the body, and if there is any shortage as a result of reduced blood flow from narrowed arteries, available oxygen is quickly used up. Vitamin A, on other hand , function effectively as an antioxidant in conditions of low oxygen concentrations, and this may account for its apparent value in these cases. It is, of course, possible that it also has valuable effects other than simply free radical trapping.

There is also the possibility that vitamin E will not pass through the walls of the smallest brain blood vessels the capillaries as easily as vitamin A. the brain capillaries are less permeable than those in other pats of the body. This is called the 'blood brain barrier' and it prevents many substances, including some drugs, from getting through. Although vitamins A and E are both fat-soluble, the molecule of vitamin E is somewhat bulkier than that of vitamin A.

A lesson to be learned from this study would seem to be that each antioxidant has its optimum range of action, and that several different antioxidants are needed to ensure comprehensive cover. It would be foolish in the extreme, however, to suppose that taking antioxidant vitamins is an effective substitute for a healthy lifestyle that minimizes the risk factors for stroke avoidance of smoking, good weight control, low intake of saturated fats, plenty of vegetables and fruit in the diet, and plenty of exercise.