Clinical Context...
Undernutrition before birth, as well as in
infancy, childhood, and adulthood, is associated with an increased risk
for stroke in later life. However, the mechanism of increased stroke
risk is poorly understood.
In addition, overnutrition also increases stroke
risk. The likely mechanism is by hastening the onset of obesity,
hypertension, hyperlipidemia, and diabetes. The objective of this review
by Hankey was to describe recent evidence regarding the effects of
nutrition on stroke risk.
Study Synoposis and Perspective
The overall quality of a person’s diet and the
balance between caloric intake and caloric expenditure appear to be more
important determinants of stroke risk than the actual foods and
nutrients consumed, according to a new review published in the January 2012 special issue of the Lancet Neurology.
In general, the 2 biggest threats to health and risk of stroke are
overeating and excess salt, author Graeme J. Hankey, from Royal Perth
Hospital, Perth, Western Australia, writes.
"These behaviors are a normal response by people to an abnormal
environment," Dr. Hankey notes. "Our living environments have become
more conducive to consumption of energy and less conducive to
expenditure of energy in developed and increasingly in developing
regions."
He writes that between 1970 and 2008, the incidence of stroke in
high-income countries fell by 42%, probably as a result of increased
public awareness about the dangers of high blood pressure, high
cholesterol, and cigarette smoking.
But in poorer countries, the incidence of stroke increased by more
than 100% during this period. This rise coincided with food and
lifestyle changes associated with industrialization and urbanization.
Small Number of Trials
In his review, Dr. Hankey examines the evidence linking nutrition and
diet to the risk of stroke. He searched PubMed articles published in
English from 1970 to October 2011, using a variety of search terms.
The review included a small number of randomized trials and large observational and epidemiological studies.
He found that the findings from these studies were diverse, owing to
the fact that most were epidemiological and therefore "prone to
substantial methodological challenges of bias, confounding, and
measurement error."
For example, one observational study found that a high intake of a
healthy diet was associated with an increased risk of stroke, whereas
another observational study found just the opposite.
Dr. Hankey's review also revealed the following effects of individual foods and beverages on the risk of stroke:
- Fish: 3 servings a day associated with a 6% lower risk of stroke
- Fruits and vegetables: >5 servings a day associated with a 26% lower risk of stroke
- Meat: Each daily serving associated with a 24% increased risk of stroke
- Reduced-fat milk: associated with a lower risk of stroke vs full-fat milk
- Chocolate: High consumption associated with a 29% lower risk of stroke
- Coffee: 3 to 4 cups per day associated with a 17% lower risk of stroke
- Tea: ≥3 cups per day associated with a 21% lower risk of stroke
- Sugar-sweetened beverages: high intake associated with increased obesity, diabetes, metabolic syndrome, and coronary heart disease
- Whole grains: high intake associated with a 21% lower incidence of cardiovascular events
- Rice: intake not associated with risk of stroke
"Further research is needed to improve the quality of evidence
relating to the association of many nutrients, foods, and dietary
patterns with stroke risk," Dr. Hankey suggests.
This requires adequately powered, large randomized trials with
carefully described patient populations and interventions. The outcomes
of such trials should also distinguish first-ever and recurrent stroke,
as well as ischemic and hemorrhagic stroke, and their different
etiologies.
Dr. Hankey also suggests that population-wide salt reduction programs
led by governments and with industry cooperation could be highly cost
effective.
"In the USA, modest, population-wide reductions in dietary salt of up
to 3 g per day…are projected to reduce the annual number of new cases
of stroke by 32,000 to 66,000, similar to the benefits of
population-wide reductions in tobacco use, obesity, and cholesterol
levels," he writes.
Dr. Hankey told Medscape Medical News that he hopes his
study will stimulate conclusive studies "by means of large, randomized
controlled trials of the effect of dietary nutrients, foods, and
patterns on stroke and its pathological and etiological subtypes."
The current evidence associating dietary nutrients, foods, and
patterns with stroke is generally suboptimal for providing reliable
conclusions about causality, he reiterated.
"The effect of only a few supplements on stroke risk have been
studied by means of large, randomized controlled trials, and all of
those have shown no benefit of antioxidant vitamins, B-vitamins, and
calcium supplements in preventing stroke, despite large, more
suboptimal, epidemiological studies claiming they should be beneficial,"
he said.
Best Diet Still Uncertain
Commenting on this study for Medscape Medical News, Eugene
Storozynsky, MD, a cardiologist from the University of Rochester Medical
Center, Rochester, New York, said that he agrees with Dr. Hankey's
conclusions.
"This is a good review of the literature as to what role diets and
their components would have on reducing stroke, and what it tells us is
that there still is a lot of uncertainty about the best diet. One study
suggests benefit of a certain food or strategy, the other may come to
the opposite conclusion," Dr. Storozynsky said.
The take-home message here is as Dr. Hankey notes, Dr. Storozynsky
continued. "We need rigorously done randomized controlled trials to
really monitor the long-term effects of diets and nutrients, rather than
observation studies that look at individual factors, to see whether or
not there is any benefit to adopting certain strategies."
Dr. Storozynsky also noted what he considers to be an important omission from Dr. Hankey's review.
"This review did not look at the effect of exercise and how it
affects nutrition or stroke results. Does routine daily exercise
mitigate the effect of intermittent poor eating? Exercise definitely
needs to be part of the equation," he said.
Helmi L. Lutsep, MD, from the Oregon Stroke Center at Oregon Health
Science University in Portland, added, "My quick read of the article
suggests that it is a very nicely written, comprehensive review of our
current knowledge regarding nutrition and stroke."
Dr. Lutsep, who is also a spokesperson for the American Academy of
Neurology, added, "While I haven't seen all of these pieces summarized
in one place before, I don't think that the article provides novel
observations."
Dr. Hankey reports that he was the principal
investigator of the VITAmins TO Prevent Stroke (VITATOPS) trial and has
financial relationships with Sanofi-Aventis, Johnson & Johnson,
Bristol-Myers Squibb, Boehringer Ingelheim, Bayer, and Pfizer Australia.
Dr. Storozynsky and Dr. Lutsep have disclosed no relevant financial
relationships.
Lancet Neurol. 2012;11:66-81. Abstract
The National Stroke Association provides a comprehensive discussion for patients about stroke prevention.
Study Highlights
- On the basis of a literature review, the reviewer noted the following findings:
- Vitamin A supplementation increases all-cause mortality risk.
- β-carotene supplementation increases cardiovascular and all-cause mortality risks and does not prevent stroke.
- Vitamin C supplementation does not prevent stroke.
- Vitamin E supplementation increases all-cause mortality risk and does not prevent stroke.
- Although folic acid supplementation does not prevent stroke in populations with high folate intake, deficiency in regions of low folate intake may be a causal and treatable risk factor for stroke.
- Vitamin D deficiency is associated with hypertension, cardiovascular disease, and stroke, but to date, supplementation has not been shown to prevent cardiovascular events. Randomized trials are underway.
- Salt supplementation by 5 g per day is linked to a 23% increase in stroke risk (95% confidence interval [CI], 6 - 43).
- Although decreasing salt intake has not been shown to reduce stroke risk, lowering consumption by 2 g per day is associated with a 20% decrease in cardiovascular events (95% CI, 1 - 36), and lower salt intake is also linked to blood pressure reduction.
- Potassium supplementation by 1 g per day is associated with an 11% reduction in the risk for stroke (95% CI, 3 - 17), but supplementation is not proven to prevent stroke.
- Potassium supplementation by 0.8 g per day is associated with a decrease in blood pressure by 5/3 mm Hg.
- Calcium supplementation exceeding 0.5 g per day is linked to a 31% increase in the risk for myocardial infarction (95% CI, 2 - 67), does not prevent stroke, and may actually increase stroke risk.
- High intake of total fat, trans fats, and saturated fats is not associated with an increased risk for stroke, and reduced total fat intake does not lower stroke risk.
- High intake of plant n-3 polyunsaturated fats is associated with a reduced risk for stroke.
- Marine n-3 polyunsaturated fat supplementation lowers cardiovascular events and death by 8% (95% CI, 1 - 15), but in a randomized trial, it did not reduce stroke risk.
- High intake of carbohydrates with high glycemic index and glycemic load is associated with increased blood glucose levels, body weight, and stroke mortality.
- High fiber intake is linked to lower blood pressure, blood glucose levels, and low-density lipoprotein cholesterol levels.
- High protein intake is not associated with stroke risk.
- High intake of a healthy diet was linked to an increased risk for stroke in one observational study and a reduced risk for stroke in another observational study.
- High intake of an unhealthy diet was linked to an increased risk for stroke and a population-attributable risk for stroke of 19% (99% CI, 11 - 30).
- In women, a prudent diet or Dietary Approaches to Stop Hypertension (DASH)–style diet is associated with a lower risk for stroke, and a Western diet is linked with a higher risk for stroke.
- In women, the Mediterranean diet is associated with lower risks for stroke, cardiovascular disease, cardiovascular mortality, and all-cause mortality.
- The effects of a vegetarian diet and a Japanese diet on stroke risk are unknown.
Clinical Implications
- Reliable evidence from randomized trials suggests that dietary supplementation with antioxidant vitamins, B vitamins, and calcium does not reduce the risk for stroke. However, methodologic limitations of studies to date preclude firm conclusions regarding the effect of many other nutrients on stroke risk.
- Less reliable evidence suggests that stroke can be prevented by prudent diets; Mediterranean or DASH-type diets; diets that are low in salt and added sugars and high in potassium; and diets that meet, but do not exceed, energy requirements. The overall quality of dietary pattern and the balance between energy intake and expenditure seem to affect stroke risk to a greater extent than individual nutrients and foods.
