Medscape Medical News
Janis C. Kelly
April 08, 2014

Regular consumption of milk was associated with slower progression of joint damage in women with osteoarthritis (OA), but regular consumption of cheese was associated with more joint damage, Bing Lu, MD, DrPH, and colleagues report in an article published online April 6 in Arthritis Care & Research.

“Dietary factors were under-researched in OA incidence and progression. It is of great public health and clinical significance to examine the role of diet on OA progression,” Dr. Lu, assistant professor of medicine, Brigham and Women’s Hospital, Boston, Massachusetts, told Medscape Medical News.

Dr. Lu said that the key finding in this study, which was the largest to investigate the effect of dairy intake on progression of knee OA, was that increased milk consumption was associated with slower progression of joint space narrowing in women with OA. Progression was also slower in men who drank 7 or more glasses of milk per week.

“The study is well done, but the results are indeed a bit puzzling. Seven servings of milk is only 1 a day, significantly less than we suggest to prevent osteoporosis, so the finding is remarkable indeed,” Professor Dr. J. W. J. Bijlsma told Medscape Medical News. Dr. Bijlsma is professor of rheumatology, University Medical Center, Utrecht, and director of the Amsterdam Rheumatology and Immunology Center, The Netherlands.

In an accompanying editorial that will be published in Arthritis Care & Research, Shivani Sahni, PhD, and Robert McLean, DSc, MPH, from Harvard-affiliated Hebrew SeniorLife Institute for Aging Research in Boston, Massachusetts, write, “This novel study not only highlights the important need for further nutrition research in OA management, but also opens new lines of inquiry that could help direct future nutrition research in the etiology of OA. Most importantly, the biological mechanism via which dairy foods such as milk may be beneficial is unclear. To clarify the mechanism, it will be important to examine the dairy-specific nutrients, which may be beneficial for OA. This area of research can ultimately lead to dietary interventions to slow down OA progression. It is vital to understand the extent to which the protective association of milk is perhaps driven by its effect on obesity rather than an anti-inflammatory or other currently unknown effect on OA progression.”

Dose-Response Relationship Between Milk and OA Joint Changes

Dr. Lu and colleagues studied the prospective association of milk consumption with radiographic progression of knee OA in 2148 participants (3064 knees) with knee OA who were recruited for the Osteoarthritis Initiative. Subjects included 888 men and 1260 women who had follow-up at 12, 24, 36, and 48 months.

The researchers evaluated OA progression, using quantitative joint space width (JSW) between the medial femur and tibia of the knee on plain radiographs. Milk consumption was assessed at baseline, using the Block Brief Food Frequency Questionnaire, which included information on milk in general, but not on different types of milk (eg, low-fat). For semiquantitative analysis, the researchers used the Osteoarthritis Research Society International grade (grade: 0, no joint space narrowing; 1, definite joint space narrowing; 3, severe joint space narrowing) to measure OA progression. The independent association between milk intake and JSW decrease over time was assessed with multivariate linear models for repeated measures adjusted for baseline disease severity, body mass index, dietary factors, and other potential confounders such as race, smoking, alcohol consumption, history of gout, obesity, physical activity, K-L grade, vitamin D intake, and calcium intake.

As milk consumption increased from none to 3 or less, 4 to 6, and 7 or more (8-ounce) glasses per week, the loss of JSW in women decreased in a dose-response manner by 0.38, 0.29, 0.29, and 0.26 mm, respectively. No association between milk consumption and JSW decrease was reported in men.

“When we included milk intake as a continuous variable, a 10 glasses increase in milk intake per week was associated with a decrease [in women] of 0.06 mm JSW change over 48 months (p=0.020). By contrast in men, we did not observe a significant inverse association of milk intake with JSW change,” the authors write.

Similarly, the scores showed that after adjustment for covariates, there was a significant inverse association between milk intake and the adjusted hazard ratios (HR) for OA progression in women. With increasing levels of milk intake, the HRs were 0.67 (95% confidence interval [CI], 0.50 – 0.91), 0.71 (95% CI, 0.50 – 1.00), and 0.56 (95% CI, 0.38 – 0.81), respectively, compared with no milk consumption (Ptrend = 0.008). In men, only 7 or more glasses per week of milk reduced the risk for OA progression.

Cheese Worsened Progression of Joint Damage

Cheese intake of more than 7 servings per week was associated with a worsening of knee OA progression. The researchers suggest this might be because of the high level of saturated fatty acids in cheese. Increased consumption of saturated fatty acids has been linked to increased bone marrow lesions, which in turn predict knee OA progression.

Calcium and OA Progression in Women vs Men

The researchers suspect dietary calcium might be a factor linking milk consumption and reduced knee OA progression. For the women in this study, the highest quartile of dietary calcium intake was associated with a significant reduction in joint space narrowing, and including dietary calcium intake in the multivariate analysis reduced the effect of milk consumption by 25%.

Calcium might also explain some of the sex difference. Average dietary calcium intake was 647 mg/day in women and 715 mg/day in men (P < .001). “If dietary calcium is a possible mediation factor to link between milk consumption and knee OA progression, women may be more sensitive for the effect of calcium intake through milk than men. However the gender differences in the relationship of milk consumption with OA progression are not completely understood,” the authors write.

“Sex differences have been noted in the prevalence, incidence, and severity of OA for many years. Faber and colleagues found cartilage thickness of the distal femur to be less in women than in men. Other evidence suggested a protective effect of exogenous estrogen on cartilage and bone turnover,” Dr. Lu said.

Dr. Bijlsma added, “There is a clear role for bone in the development and/or progression of OA. I would assume that the effect of milk will be via bone; however, the vitamin D status is of relevance here as well. In addition, bone turnover is more sensitive to change in women than in men, which may explain differences found between men and women. A clear explanation is still missing; some epidemiological studies might help here.”

Dr. Lu concluded, “A healthy diet, including frequently drinking fat-free or low-fat milk, would be beneficial to your knees and general health.”

Funding for this analysis was provided by the National Heart, Lung and Blood Institute. The authors and Dr. Bijlsma have disclosed no relevant financial relationships.

Arthritis Care Res. Published online April 6, 2014. Article abstract

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