Fermented dairy intake and symptomatic radiographic knee osteoarthritis risk in middle-aged and older adults: An 11-year cohort study.

BACKGROUND AND AIMS: Dairy products are considered beneficial for musculoskeletal health, but limited evidence supports their benefits on knee osteoarthritis (KOA) prevention. This study aimed to examine associations between total and specific dairy product intake and the risk of KOA in East Asian adults. METHODS: This 11-year cohort study included 10,411 community-dwelling Japanese individuals aged 40-74 years. Demographic data, body size, information on lifestyle factors, and medical history were collected using a self-administered questionnaire at the baseline survey conducted in 2011-2013. A validated semi-quantified food frequency questionnaire was used to assess the intake of total dairy products, milk, and fermented dairy products (cheese and yogurt). Energy-adjusted intake was calculated using the residual method. Incident symptomatic radiographic KOA, defined as Kellgren-Lawrence grade ≥2 among individuals presenting with knee symptoms, was ascertained by participating medical institutions. Cox proportional hazards models were used to estimate adjusted hazard ratios (HRs). RESULTS: Mean age of participants was 57.9 years. Median intakes (g/day) of milk, cheese, yogurt, and total dairy products were 27, 1, 8, and 118, respectively. Higher quartiles of total dairy intake were associated with lower hazards of KOA (P for trend = 0.0174), with the third (HR = 0.81, 95%CI: 0.67-0.99) and fourth (HR = 0.79, 95%CI: 0.65-0.97) quartiles having lower hazards than the first quartile. Similarly, higher levels of fermented dairy intake were associated with lower hazards of KOA (P for trend = 0.0007), with the third (HR = 0.81, 95%CI: 0.67-0.99) and fourth (HR = 0.72, 95%CI: 0.58-0.87) intake groups having lower hazards than the zero intake group. Similar trends were observed in sex-stratified analyses (P for trend = 0.0396 for males, 0.0081 for females). Whereas no association was observed for milk intake (P for trend = 0.1615), the frequencies of cheese and yogurt intake were independently associated with KOA hazards (P for trend = 0.0228 and 0.0272, respectively). CONCLUSIONS: Higher dairy intake is associated with a reduced risk of KOA among middle-aged and older individuals with relatively low dairy intake. The observed association appears to be largely driven by the intake of fermented dairy products rather than milk.