Divorce, job loss and other big changes in your life can expose some big patches of scalp. So can chronic, everyday stresses - missed deadlines, angry bosses.

And if hair loss is in your genes, stress can increase the production of androgens, the male sex hormones destined to kill your follicles.

"If increased androgens cause hair loss, stress may make balding worse," says Dr Proctor.

Reducing your stress levels might cut production of androgens and slow your hair loss, but it won't make a single hair grow back. Hair lost to a boost in sex hormones during a period of manic stress is gone for good.

By the time smokers turn 40, many sport the withered hair follicles and lousy comb overs of much older men.

Smoking may play the same role in hair loss as it does in heart disease, says Dr Proctor. Tobacco smoke damages the linings of blood vessels, which produce less nitric oxide, and this might short circuit hair growth.

Smoking also constricts blood vessels and hinders circulation, says Dr Wilma F Bergfeld, head of clinical research in the department of dermatology at the Cleveland Clinic, in the US.

Diminished blood flow 'ages' hair follicles prematurely.

And while these findings are based on cigarette smokers, it's a good bet cigars won't do a hairline much good either.

American men, researchers from the University of Texas at Houston and Boston University in the US found that those with the least hair also had the highest risk of dying from heart disease.

Another study of 872 Italian factory workers found that those who were balding had higher cholesterol levels than did the men who didn't show signs of hair loss.

Hair loss and heart disease are evidently linked.

"Bald men are more than three times as likely to suffer a heart attack as men with a full head of hair," says Dr Peter Proctor, a dermatologist and research pharmacologist in Houston, in the US.

The connection is likely due to nitric oxide, a naturally occurring chemical that prevents blood clots and dilates blood vessels (two keys to avoiding heart attacks). Nitric oxide also seems to foster hair growth and erections.

When atherosclerosis damages the walls of your blood vessels, it causes them to produce less nitric oxide. Some physicians think this same deficiency may also trigger hair loss.

"If your blood vessel linings aren't damaged by atherosclerosis, normal hair growth might continue," says Dr Proctor.

So eating a low fat diet and plenty of fish (which deliver heart healthy omega-3 fatty acids), and exercising three times per week won't just keep you thinner and alive longer