Student or Learner
The findings suggest that the effect of depression on heart health may have less to do with changes in hormones or other biochemical pathways, and more to do with behavior. Compared with other people, notes Whooley, the depressed are less healthy overall — they're less likely to exercise or take their heart medications, and are more likely to smoke. The relationship also feeds back on itself; previous studies show that exercise not only improves cardiovascular health, but also elevates mood and can ease depression.
I can't understand the exact meaning of the sentence in bold above.
( the whole story of this article is here: How Depression Harms Your Heart - TIME)
The relationship is a cause and effect:
Depression causes people to exercise less and live unhealthy lifestyles.
cause = depression
effect = exercising less and unhealthy lifestyles
"The relationship also feeds back on itself" (I agree with you is very akward) suggests that the relationship can be inverted so that effects can be causes and causes can be effects. Therefore you get a new cause and effect relationship that is opposite of the original.
Exercising more combined with healthy lifestyles lowers depression.
cause = exercising more (opposite the original)
effect = less depression (opposite the original -- the ANSWER to the problem)
I can only guess why the author used the expression "feeds back on itself" except to suggest that the answer to the dilemna is in the original relationship but with some tweaking.