BOSTON (Reuters) – Vigorous exertion does indeed dramatically increase the chances of having a heart attack, a new study has found.

But, but vigorous, long-term exercise provides so much protection against heart disease, the risk is more than worth it, according to the 12-year study of 21, 481 male physicians.

Dr. Christine M. Albert of Brigham and Women’s Hospital in Boston led the team that examined data from the Physicians’ Health Study, begun in 1982.

They found that the chance of a man dying during a particular exercise session was 1 in 1.5 million.

The risk varied dramatically.

Men who engaged in vigorous exercise less than once a week were seven times more likely to die suddenly during or immediately after working up a sweat than someone who exercised at least five times a week.

“The benefits of a physically active lifestyle” in terms of warding off heart disease “clearly outweigh the small risks,” Albert and her team conclude in a study published in today’s New England Journal of Medicine.

In an editorial in the Journal, Dr. Barry J. Maron of the Minneapolis Heart Institute Foundation said the results “substantiate the paradox of exercise – that vigorous physical exertion can be regarded as a two-edged sword; it can simultaneously increase the short-term risk of sudden death (as a result of underlying heart disease) and also offer protection from this risk in those who regularly engage in exercise.”

Published Toronto Star