Over-exercising may be risky for heart attack survivors, researchers warned today.
Regular exercise is thought to lower the risk of death from diseases including hypertension, stroke, and type 2 diabetes.
Current US guidelines recommend about 150 minutes a week of moderate-intensity exercise, or about 75 minutes of vigorous-intensity exercise. However, evidence also exists of an increase in cardiovascular deaths in heart attack survivors who exercise too much.
So Dr Paul Williams of Lawrence Berkeley National Laboratory, California, USA, and his team looked at the link using figures on about 2,400 heart attack survivors. Their long-term study confirmed previous findings that the cardiovascular benefits of walking and running are equivalent for the same energy expenditure, though it takes twice as long to burn the same calories when walking than running.
Over time, people who ran 30 miles or walked 46 miles a week had a 65% lower risk of death from cardiovascular events than those who did no exercise. The benefit increased alongside increased exercise. But above this level of exercise, the benefit tended to fall.
Findings appear today (13 August) in the journal Mayo Clinic Proceedings. Dr Williams stated: "These analyses provide what is to our knowledge the first data in humans demonstrating a statistically significant increase in cardiovascular risk with the highest levels of exercise.
"Results suggest that the benefits of running or walking do not accrue indefinitely and that above some level, perhaps 30 miles per week of running, there is a significant increase in risk. Competitive running events also appear to increase the risk of an acute event."
But they add that the study participants had all previously survived a heart attack, and do not represent the whole population.
Amy Thompson, of the British Heart Foundation, said most people should not be alarmed by the findings.
She said: "This study suggests if you’ve had a heart attack you may be putting yourself at risk of another if you participate in vigorous exercise above the recommended amounts – such as running for more than 30 miles per week.
“We shouldn’t be alarmed just yet, the study failed to include people free of heart disease and further research is needed before we can draw any firm conclusions. In the mean time we should all try and build exercise into our daily routines to keep our hearts healthy."
Williams, P. T. et al. Increased Cardiovascular Disease Mortality Associated With Excessive Exercise in Heart Attack Survivors. Mayo Clinic Proceedings 13 August 2014 doi: 10.1016/j.mayocp.2014.05.006).
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