A mineral supplement derived from seaweed may help people with knee arthritis cut down on painkillers, a preliminary study suggests.

Researchers found that among 22 adults with moderate to severe knee arthritis, those who took the supplement for 12 weeks were able to reduce their use of non-steroidal anti-inflammatory drugs — commonly known as NSAIDs — but still show improvements in walking ability and range of motion in the knee joint.

More studies are needed, the researchers report in the online publication Nutrition Journal, but these early results suggest that the seaweed supplement — sold as Aquamin — could reduce some patients' need for painkillers.

Dr. Joy L. Frestedt, of Frestedt Inc., in St. Louis Park, Minnesota, led the study. Frestedt Inc. is a consulting firm that runs clinical trials. Ireland-based Marigot Ltd., which markets Aquamin, funded the study.

The study included 22 older adults with knee osteoarthritis, the wear-and-tear form of arthritis in which the cartilage cushioning the joints gradually breaks down. The patients were randomly assigned to take either Aquamin or inactive "placebo" capsules for 12 weeks.

After the first two weeks of treatment, all patients were asked to cut their NSAID use in half for the next two weeks, then stop the drugs completely for the rest of the study.

In general, Frestedt's team found, Aquamin patients performed better on tests of walking distance and knee joint range of motion after one month of treatment, despite their NSAID use being halved.

The benefits did not continue, however, once the patients stopped taking NSAIDs altogether, the study found. Six patients dropped out of the trial because of worsening pain — though five of them were in the placebo group, the researchers note.

The findings, they write, indicate that Aquamin "cannot entirely replace" NSAIDs as a treatment for knee arthritis.

It's not fully clear why the seaweed supplement might aid arthritis symptoms. It contains a mix of trace minerals, with the main ingredients being calcium and magnesium.

Some of those minerals, Frestedt and her colleagues say, have been shown to have anti-inflammatory effects in lab animals. For its part, calcium is known to boost bone mineral density, and there is some evidence that it may ease arthritis symptoms as well.