Nov. 14, 2012 -- Men with osteoarthritis of the knee may want to avoid sugar-packed soft drinks. That's the advice of researchers who found that drinking sugary soda is associated with progression of the disease in men.
No such link was found in women in the study of more than 2,000 people with knee osteoarthritis.
"Our main finding is that in general, the more sugary soda men drink, the greater the risk that knee osteoarthritis will get worse," says researcher Bing Lu, MD, DrPh. Lu is assistant professor of medicine at Harvard Medical School and associate biostatistician at Brigham and Women's Hospital in Boston.
If you're thinking that is because the calories in soda may contribute to being overweight or obese -- a known risk factor for knee osteoarthritis -- think again.
Much to the researchers' surprise, the link between knee osteoarthritis and sugary soft drinks could not solely be explained by weight, Lu says.
"We very carefully [took into account] weight in the statistical analysis. We controlled not only for the general categories of overweight and obesity, but also for patients' specific body-mass indices, or BMIs," he says.
When the men were divided into obese and non-obese, the link between sugary drinks and worse knee damage held true only in the non-obese men.
This suggests that soft drinks worsen knee osteoarthritis independently of the wear and tear on the joints caused by carrying around excess weight, Lu says.
What Is Osteoarthritis?
In people with osteoarthritis, the cartilage in a joint wears away in some areas. The function of cartilage is to reduce friction in the joints and serve as a "shock absorber." The wearing away of cartilage leads to pain and other symptoms.
Nearly one in 100 people have evidence of knee osteoarthritis on X-ray. And nearly 19% of women and 14% of men over age 45 have joint pain, stiffness, and other symptoms of knee osteoarthritis, according to a 2007 study.
In addition to obesity, known risk factors include:
- Older age
- Prior injury to the knee
- Extreme stress to the joints
The study was presented this week at the American College of Rheumatology Annual Meeting in Washington, D.C.
Suggestions From Experts
So what's a man who enjoys soda to do?
"There's an easy answer. Just don't drink [sugary] soda," Lu says. He notes that some studies have also linked soda to heart disease.
Another expert says that's going too far. "As with everything, enjoy soda in moderation. If you are [a man with] knee osteoarthritis and are drinking a lot of soda, this might be a reason to curb back," says American College of Rheumatology spokesman Scott Zashin, MD. Zashin is a clinical professor of internal medicine in the rheumatology division at the University of Texas Southwestern Medical School in Dallas.
The study doesn't prove cause and effect, Zashin notes. As with any study presented at a medical meeting, it has not been thoroughly reviewed by experts. The findings need to be repeated before any recommendations to patients can be made, he says.
What is known is that in people with knee osteoarthritis, every excess pound of weight is 4 extra pounds of dead weight on the knee joint, Zashin says. "So concentrate on your overall diet and weight, not one component."
Beverage Industry Perspective
The American Beverage Association (ABA), the trade association representing non-alcoholic beverages in the U.S., took issue with the findings.
In a statement, the ABA writes: "The authors' 'novel findings' -- as they call them -- suggest only a possible association of soft drink consumption with osteoarthritis in knees, which they state cannot be proven without further testing. Consequently, this presentation fails to establish that drinking soft drinks causes any negative health outcomes or even that they are linked to negative health outcomes."
The ABA statement goes on to say: "As stated by the NIAMSD (National Institute of Arthritis and Musculoskeletal and Skin Disease), overweight and obesity may impact overall joint health. However, all calories count when it comes to overweight and obesity, and there is nothing unique about the calories contributed to the diet by soft drinks."
Lu says that certain ingredients in sugary sodas, including phosphoric acid, caffeine, and ingredients for coloring and sweetening, may affect absorption of bone-building calcium and bone health. But that remains to be studied.
As for why the findings did not apply to women, Lu says: "It is unclear why the results were different between men and women. It could be due to sex hormones. For example, estrogen has been associated with cartilage degeneration. Further research is needed to understand the pathways."
No conclusions can be drawn about diet soda and knee osteoarthritis, as that wasn't studied.
How the Study Worked
Lu and colleagues reviewed the records of 2,149 men and women who participated in a large osteoarthritis study. They were determined to have knee osteoarthritis by X-ray.
At the beginning of the study, all filled out dietary questionnaires that asked how many soft drinks, not including sugar-free beverages, they drank on average each week.
Every year for four years, the researchers tracked their osteoarthritis progression by measuring the space between the joints. The more cartilage that is lost, the less the space. BMI was also measured.
After taking into account BMI and other risk factors for knee osteoarthritis, men who drank five or more soft drinks a week had twice as much narrowing of joint space compared with men who did not drink sugary soda.
Funding for the study was provided by the National Institutes of Health. Funding partners included Pfizer, Inc.; Novartis Pharmaceuticals Corporation; Merck Research Laboratories; and GlaxoSmithKline. They all make anti-arthritis drugs.
These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.