For years, family doctors have been pestering their patients about diet and exercise to improve their health. Now, if recent studies are any indication, they may start pestering people about the company they keep.

According to a joint study by Brigham Young University and the University of Utah, published in "The Annals of Behavioral Medicine," ambivalent and unpredictable friendships can make you ill. They raise blood pressure and wear down resistance. On the other hand, good friendships help you relax and handle life more efficiently.

For years, of course, researchers have known that personal relationships affect people's physical well-being. It has been shown that single men die sooner than most and happily married couples tend to live extended lives. Now, the influence of personal connections is going beyond the family and reaching into society.

We think that's a healthy trend.

Ironically, many people fret over calories and take supplements but live lives that are in constant turmoil. Ironing out differences with family and selecting associates who have a positive affect on one's state of mind may well do as much to lengthen years and create a healthy lifestyle as many of the trendy and expensive alternatives.

We urge researchers at BYU and the U. to press ahead with further studies, expanding them as they go. The more we know about the ways our interaction with others affects us personally, the closer society moves to seeing harmony and mutual respect as the best "self-interested" way to improve one's own lot.

Somehow, subconsciously, people have always suspected as much. The cliches about wayward children, unfaithful spouses and back-stabbing friends driving people "to an early grave" have been around for centuries. Now, however, thanks to controlled experiments, scientists are beginning to discover the truths hidden in such statements.

Good fences may make good neighbors. But good neighbors make for good health.

People have always known that. Now they're getting hard data to back it up.