The metabolic syndrome’s association with the development of osteoarthritis appears to occur primarily through the influence of factors related to body weight or body mass index, according to an analysis of data from the longitudinal Framingham osteoarthritis study.

Jingbo Niu, DSc, of the Clinical Epidemiology Research and Training Unit at Boston University, and her colleagues found that while the presence of the metabolic syndrome (MetS) and its individual components – central obesity, dyslipidemia, impaired fasting glucose, and hypertension – were associated with a risk of both radiographic osteoarthritis (ROA) and symptomatic OA (SxOA), all associations besides high blood pressure (particularly diastolic blood pressure) disappeared after they adjusted for body mass index (BMI) or body weight ( Arthritis Rheumatol. 2017 Mar 3. doi: 10.1002/art.40087 ).

Previous studies have found a strong and consistent relationship between MetS and an increased risk of knee OA before adjustment for BMI, and even after adjustment for BMI some of the components of MetS, mostly central obesity and hypertension, have persisted. But very few of these studies have been longitudinal and most have not focused on incident SxOA, the investigators said.

The research team analyzed 991 participants of the 1992-1995 Framingham Offspring Cohort who did not have existing OA at baseline. Average age was 54.2 years; 55.1% were women. According to Adult Treatment Panel III criteria, 27% of the men and 23% of the women had MetS. Those who had MetS were older, had a higher BMI, and were less likely to drink alcohol or have a college education.

In 2002-2005, the cohort underwent follow-up for the presence of OA. The incidence of ROA in the cohort was 9.8% (78 of 800 knees) in men and 10.5% (105 of 1,003 knees) in women. ROA occurred when a knee without previous radiographic evidence of OA developed a Kellgren and Lawrence score of 2 or higher, and SxOA occurred when a knee developed ROA together with knee pain.

After adjusting for age, education, smoking status, alcohol consumption, and physical activity, the researchers found that MetS, abdominal obesity, and low high-density lipoprotein cholesterol were significantly associated with incident ROA among men. Among women, abdominal obesity and high blood pressure were associated with incident ROA, while MetS was not. However, after adjustment for body weight or BMI, none of the associations remained significant.

The incidence of SxOA was 6.3% (53 of 837 knees) in men and 7.2% (75 of 1,037 knees) in women. Incident SxOA was significantly associated with MetS in women and with the MetS components of abdominal obesity and high blood pressure in both men and women before adjustment for BMI or body weight. However, only an association between diastolic blood pressure and incident SxOA persisted in both sexes after adjustment for body weight, the study authors noted.

“High blood pressure is another MetS component associated with OA in previous studies before adjusting for BMI … While we found [diastolic blood pressure] was related to incident SxOA even after adjustment for BMI, the relation of [systolic blood pressure] and incident SxOA was nearly significant also, suggesting that both might be related to SxOA,” the study authors wrote.

But a cross-sectional analysis of the relationship would be challenging to interpret, they said, since treatment for SxOA included NSAIDs, which are known to raise blood pressure.

The National Institutes of Health supported the study. The authors declared having no conflicts of interest.