Last month, the Wall Street Journal released a controversial article entitled "The Potential Cardiac Dangers of Extreme Exercise ," which revisited a question I've explored before: How much exercise is too much ?

But this study unveiled new findings -- specifically the disturbing news that exercise that is extreme in volume and intensity is associated with high levels of atherosclerotic plaque in the coronary arteries. More specifically, the study that the article reports on looked at 169 veteran competitive endurance athletes and compared them to a control group of 171 relatively sedentary subjects. The study revealed lower levels of coronary artery calcium -- a significant risk factor for heart disease -- in athletes who ran fewer than 35 miles a week or cycled fewer than 100 miles a week. But the group who ran or cycled beyond that volume were found to have higher levels of coronary artery calcium than did the control group.

In addition to excess volume creating coronary artery issues, the study discovered an association between coronary calcium levels and exercise intensity. Compared with the control group, the study found significantly lower levels of coronary calcium in the men and women who exercised at lower intensities. In both men and women, coronary calcium levels rose as speed increased, and the fastest men had especially higher levels of coronary calcium.

Granted, the type of plaque found within the heavy exercisers was "dense" plaque, which opposed to soft plaque, may be somewhat less likely to rupture and cause a heart attack or stroke. But it was plaque nonetheless! So what does all this mean? Should you ditch your goal of running a marathon, and also stay far away from triathlons, that cycling tour of Italy you've always wanted to do, or long bouts on a treadmill at the gym?

While I've certainly acknowledged in my previous article on this topic that from a health and longevity standpoint (not necessarily a competitive and performance standpoint), there is a law of significantly diminishing returns and increased health risks when exercise exceeds about 90 minutes a day, I have a few additional, important observations for you based on this most recent date.

1) Diet Matters

Unfortunately many endurance athletes use the rigor of training and a speedy metabolism to justify a diet that is incredibly calorie dense (as it should be), but is also high in processed or sugar-laden foods. For example, common traditional foods for fueling endurance sports include high carbohydrate sources such as orange juice, bagels, cereal, crackers, bread, pasta, scones and fruit smoothies. With the advent of commercialized sports nutrition, the dietary staples of an many endurance athletes now also include sports bars and cookies, gels, powders, gummy chews and specially formulated "energy" drinks.

But a diet high in these type of refined carbohydrates can cause excessive levels of glucose in the bloodstream, a condition known as hyperglycemia . During exercise, the excess glucose is used for energy. But many endurance enthusiasts continue to consume these type of high-carbohydrate foods, even outside training. Several studies have demonstrated a link between hyperglycemia and production of free radicals by immune cells. These free radicals can not only cause inflammation, but also increase potential for insulin resistance, damage the immune system, and reduce exercise recovery . In addition, an enormous number of chronic diseases have been linked with hyperglycemia .

When this diet-based inflammation is combined with muscle tissue inflammation from repetitive motion training such as hundred mile bike rides and twenty mile runs, the body is constantly barraged with damaging free radicals. As a result of chronic inflammation, an athlete may experience constant fatigue, sore joints, disrupted sleep patterns, and frequent sickness. New studies on plaque formation in the coronary arteries has even suggested that refined sugars may play a larger role than saturated fat in dangerous LDL cholesterol production.

But the problems don't stop with refined sugar consumption. For example, an extremely high daily calorie intake also increases the likelihood of consuming large amounts of common food allergens such as dairy, wheat, whey, soy and eggs. As a result, many endurance athletes experience bloating, gas, constipation, skin problems and increased susceptibility to colds and flu. These immune system difficulties are often chalked up to "hard training." However, even when the high volume of training finally does subside, many of these problems can continue to cause a triathlete to experience poor health and gain significant amounts of fat (leading to the ever-growing population of overweight or sick ex-endurance athletes).

Finally, as proven in this quite comprehensive recent study (which I admittedly participated in), you don't actually need heavy amounts of calories or sugar to fuel endurance exercise. I'd be very interested to see the coronary calcium scores of athletes who eschew processed sugars and instead adopt a more healthy fat-based diet.

Now, so far you've just learned one reason that there may be more to this article than meets the eye. Next week, we'll delve into two more reasons why cardio may, or may not, be slowly killing you. But in the meantime, leave your comments below if you have your own thoughts to add!