Acupuncture has a "small but significant" benefit for people with low back pain and is a cost effective treatment, two studies suggest.

Low back pain is one of the most common medical problems, and is costly in terms of lost productivity and health-care benefits.

In the ancient Chinese treatment acupuncture, fine needles are placed into the skin at specific points to stimulate improved health.

Researchers studied 241 adults in Britain who had persistent, non-specific low back pain for four to 52 weeks.

The participants were randomly assigned to receive 10 sessions of acupuncture or the usual care of pain medication, physiotherapy and exercises for three months.

People who were treated with acupuncture reported less pain after 24 months of follow-up compared with the standard care group, Hugh MacPherson of the University of York in England and his colleagues reported in Friday's issue of the British Medical Journal.

After 24 months, those who received acupuncture were also less likely to report worry about their back pain and current use of pain medication. They were also more likely to report no pain for the previous 12 months.

The differences, though small, "represent a clinically worthwhile benefit and can be viewed as a 'moderate' effect," the team concluded.

The researchers did not use a placebo group with sham acupuncture, where patients feel some sensation from a needle but it isn't actually inserted.

An earlier study this year found people with low back pain who received acupuncture reported better pain control than those who did not, but not compared with people who received sham acupuncture.

MacPherson and his colleagues said more research is needed to determine the best timing for acupuncture treatments, as well as if the procedure can help when low back pain recurs.

Although acupuncture is more expensive than standard care, a second paper accompanying MacPherson's study concluded the procedure appeared to be cost effective, when quantity and quality of life benefits are considered.