High blood pressure, diabetes, cancer -- we are taught to catch diseases early by getting screened and getting tested. But is it always the right thing to do?

Anywhere from one-fifth to nearly one-third of tests and treatments are estimated to be unnecessary, and they may lead to dangerous side effects.

Dartmouth’s Dr. Gilbert Welch says we all have abnormalities in our bodies, but most are harmless.

"And thereby, some people are being treated for things that will never bother them. And yet they can be harmed by treatment," said Dr. Welch.

A recent study out of Norway estimates between 15 and 25 percent of breast cancers found by mammograms would not have caused any problems during a woman’s lifetime, but were treated anyway.

"Maybe not starting mammograms at age 40 and starting them at age 50 and maybe not doing them every year but doing them every other year might actually be in their interest," said Dr. Welch.

He also believes there’s too much testing for prostate cancer.

"20 years ago, a simple blood test was introduced called the prostate specific antigen and 20 years later about a million men have been diagnosed with a cancer that was never going to bother them," he said.

Americans receive the most medical radiation in the world, and much of it comes from repeated CT scans. Too many scans increase the risk of cancer.

Thousands of people who get stents for blocked heart arteries should have tried medication first.

Doctors prescribe antibiotics tens of millions of times for viruses like colds that drugs can not help. Back pain is the No. 1 over-treated condition, from repeated MRI scans that can not pinpoint the trouble to spine surgery on people who could have gotten better without it.

In a recent medical survey, 42 percent of primary care physicians thought their patients were over-treated. The reasons include malpractice concerns and not enough one-on-one time with patients.

About 28 percent of the doctors in the survey admitted to practicing too aggressively.