Too much exercise can kill you, scientists have revealed.

White men who work out at least 7½ hours a week are nearly twice as likely to suffer from heart disease as those who do a moderate amount, a new study shows.

Researchers in Chicago compared 25-year exercise patterns and made the surprising discovery that very active white men are 86 percent more likely to experience a buildup of plaque in the heart arteries by middle age.

But this didn’t apply to black men, they discovered.

It was suggested that high levels of exercise over time caused stress on the arteries, leading to higher coronary artery calcification, also known as CAC.

However, scientists warned that people should not stop exercising.

The team from the University of Illinois at Chicago and Kaiser Permanente looked at the physical activity trajectories of 3,175 black and white participants in the longterm CARDIA study and assessed the presence of CAC.

The presence and amount of CAC is a significant warning sign to doctors that a patient may be at risk for developing heart disease and a signal to consider early preventive care.

Deepika Laddu, assistant professor of physical therapy at the UIC College of Applied Health Sciences, said: “We expected to see that higher levels of physical activity over time would be associated with lower levels of CAC.”

However, they found that at the top level of exercise, there was no extra risk for black men, but an 86 percent increased risk for white men.

Unique to the new study is the evaluation of long-term exercise patterns, from young adulthood into middle age.

The study group had eight follow-up examinations over 25 years, from 1985 through 2011, starting at age 18 to 30 and finishing at 43 to 55.

Researchers split participants into three distinct groups, based on physical activity patterns.

Group one was defined as exercising below the national guidelines of less than 150 minutes a week, group two as meeting the national guidelines of 150 minutes a week and group three was exercising three times above the national guidelines of over 450 minutes a week.

Overall, those in group three were 27 percent more likely than those in group one to develop CAC by middle age.

When these findings were divided by race and gender, they found that white men were at the highest risk as they were 86 percent more likely to have CAC.

There was no higher odds of CAC for black participants who exercised at this level, and while there was a similar trend for white women, it was not statistically significant.

Laddu added: “Because the study results show a significantly different level of risk between black and white participants based on long-term exercise trajectories, the data provides rationale for further investigation, especially by race, into the other biological mechanisms for CAC risk in people with very high levels of physical activity.”

Study co-author Dr. Jamal Rana, a cardiologist at Kaiser Permanente in Oakland, said, “High levels of exercise over time may cause stress on the arteries, leading to higher CAC.”

“However, this plaque buildup may well be of the more stable kind, and thus less likely to rupture and cause heart attack, which was not evaluated in this study.”

However, he added: “It does not suggest that anyone should stop exercising.”

The findings were published in the journal Mayo Clinic Proceedings.