Sleeping on a hard mattress may worsen back pain.

A recent study, reported on the April 1 issue of Spine, assigned 160 subjects with chronic low back pain to sleep on one of three different types of beds for one month: a waterbed, a body-conforming foam mattress and a firm futon.

Those who slept on the waterbed or body-conforming foam mattress had significant reductions in back pain. Total sleep time was also better for those who slept on the softer mattresses.

On the other hand, those who slept on the futon tended to have increased pain and decreased sleep time. At least some of these subjects dropped out of the study because they thought the mattress was making their back pain worse.

Mattresses are commonly thought to affect back pain, especially for people whose pain is worse in the morning. Only a few studies have addressed the effects of mattresses on back pain, however, and they have had inconclusive results. These new results suggest that the waterbed and foam mattress do reduce pain and improve sleep for patients with chronic low back pain. The results are consistent with another recent study, which also found that soft mattresses had beneficial effects.

The researchers, Dr. Kim Bergholdt and colleagues, emphasize that the two types of soft mattresses studied conform to natural body curvatures. They bring the joints into intermediate positions, rather than just letting the body parts sink, which may put the joints into awkward or twisted positions. "Thus, body-conforming soft mattresses seem to have an advantage over hard mattresses," they concluded.

"Probably they are also better than soft, worn-out spring mattresses, hammocks, and other soft types that do not conform to natural, intermediary positioned body curvatures."