"We know vitamin D deficiency is a common cause of chronic, nonspecific musculoskeletal pain including chronic low back pain," Plotnikoff said.
Wilkens took issue with the assumption that Norwegians are lacking vitamin D, and said his team felt before carrying out the study that vitamin D levels "were not going to affect the results."
Taking the larger view of glucosamine, Dr. Charles Kim, a specialist in integrative medicine and acupuncture at New York University Medical Center, said "the jury is still out." He also said some types of lower back pain that involve loss of cartilage at the joints may be more likely to respond to glucosamine.
K. Simon Yeung, a pharmacist and manager of the About Herbs website for Memorial Sloan Kettering Cancer Center, called the study well-done, but said Wilkens and his co-authors were looking at the wrong target for glucosamine. He noted that the knees and hips -- joints for which glucosamine has been shown to have some effect -- have lots of movement. "The spinal column doesn't seem to have that motion," he said.
Although some of his patients have used glucosamine, Dr. Andrew J. Haig, director of the spine program at the University of Michigan, said he never thought it helped.
"The psychological damage done by a doctor flailing around, trying any of the hundreds of unproven treatments when patients often do well on their own, is not worth the possible benefits," Haig said. The new study demonstrates "that again, a lot of seemingly-reasonable treatments are not useful."
Dr. Brian Berman, director of the Center for Integrative Medicine at the University of Maryland School of Medicine, said he doesn't recommend glucosamine for lower back pain, partly because it doesn't respond to a single approach. "It's highly unlikely that there is a single magic bullet, including glucosamine, to treat this perplexing disorder."
The study reinforces the notion "that there is no 'magic pill' that can replace the common-sense treatments of exercise and weight control for relief of musculoskeletal pain," said Dr. Mark Brown, chairman of orthopedic surgery at the University of Miami.