Outside the Beltway

Causation And Correlation

Kate McMillan · Sunday, February 6, 2005 · 1 comment

The caution against linking correlation with causation has been around for a long time. Unfortunately, it isn’t invoked as often as it should be.

For decades we’ve been encouraged by health officials and professionals to exercise regularly to maintain cardiovascular health. Now, a study released at the University of Michigan involving rats indicates that there may be more involved than just working up the motivation to get off the couch.

Rats that were “born to run” not only outpaced their less-talented cousins but also were naturally less prone to heart disease, a finding that may help explain why exercise prevents heart death, researchers said on Thursday.

The study may be bad news for people who hate to exercise, suggesting that not only laziness but also their genes may put them at higher risk of heart disease.

“The reality of having a genetic determinant of our existence is that there are some people who are born with less ability to take up oxygen and transfer energy than others,” said Steven Britton of the University of Michigan.

Britton and colleagues bred rats for 11 generations to be good or poor runners.

Their high-capacity runners can exercise on a little rodent treadmill for 42 minutes on average before becoming exhausted, while the low-capacity runners average only 14 minutes.

Colleagues in Norway examined the rats for heart health factors.

“We found that rats with low aerobic capacity scored higher on risk factors linked to cardiovascular disease — including high blood pressure and vascular dysfunction,” said Ulrik Wisloff, a professor of exercise physiology at the Norwegian University of Science and Technology in Trondheim.

“Rats with low aerobic capacity also had higher levels of blood fat disorders (such as high cholesterol), insulin resistance (a pre-diabetic condition) and more abdominal fat than high-capacity rats,” added Sonia Najjar, of the Medical College of Ohio in Toledo.

“Compared to high-capacity rats, the low-capacity rats had lower levels of oxidative enzymes and proteins used by mitochondria to generate energy in skeletal muscle,” Najjar said in a statement.

Studies have shown that a poor ability to exercise aerobically — the kind that makes for heavy breathing — is a very strong predictor of heart disease, the researchers noted.

Another bit of “conventional wisdom” about health and wellness that may be due for reconsideration – especially in a day and age when governments are busy trying to effect behavior modification through legislation, under the guise of reducing health care costs.