The dangers of smoking are well documented and widely known nowadays. But here's one you probably didn't expect.

Men with osteoarthritis in the knee experience more severe pain and more loss of cartilage if they smoke.

"This is a novel finding," said Dr. Shreyasee Amin, a rheumatologist at the Mayo Clinic lead researcher in a new study that will be published online this week in the Annals of the Rheumatic Diseases.

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Knee osteoarthritis is one of the leading causes of disability in older people.

The study involved imaging the knees of 159 men with osteoarthritis and asking them about their pain.

On a pain scale with 100 as the highest score, the smokers came in at about 60 on average — with the non-smokers at 45.

The researchers don't know why smoking exacerbates the arthritis. But they suggest some possibilities. Smoking might:

— disorder cells and inhibit cell proliferation;

— increase oxidant stress, which contributes to cartilage loss;

— raise carbon monoxide levels in blood, contributing to tissue hypoxia (insufficient blood oxygenation), which could impair cartilage repair.

It is also possible, they say, that smoking lowers a person's pain threshold.

Whatever the cause and connection, the scientists are excited because smoking is, as they term it, a "modifiable risk factor."

Stop smoking, and perhaps the joints will benefit.

Another study out today suggests one way to quit: Cut back.

Researchers looked at 19 previous studies and found that in 16 of them, cutting back, combined with nicotine-replacement products, led to an increase in the ability to kick the habit.

"Cutting back is approved as a method of quitting in several European countries, but not in the United States," said study leader John Hughes, a professor of psychiatry at the University of Vermont College of Medicine. "Our review contradicts the commonly held belief that quitting requires stopping abruptly and provides evidence that smokers can quit successfully by reducing the amount of cigarettes smoked.

"Furthermore," he added, "our review indicates cutting back is often a great way to start changing smoking that can lead to eventual quitting."

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