Women who drank milk regularly had less progression of knee osteoarthritis, data from the Osteoarthritis Initiative showed.

by Nancy Walsh, Senior Staff Writer, MedPage Today
May 29, 2014

Women who drank milk regularly had less progression of knee osteoarthritis (OA), data from the Osteoarthritis Initiative showed.

Compared with women who never drank milk, whose decrease in joint space width was 0.38 mm over 4 years, those who drank up to six glasses per week had decreases of 0.29 mm, and those whose weekly consumption was seven glasses or more had decreases of 0.26 mm (P for trend=0.014), according to Bing Lu, MD, DPH, of Harvard Medical School, and colleagues.

This finding was observed only in women; no dose-response relationship was seen for men (P for trend=0.618), the researchers reported in the June Arthritis Care & Research.

An estimated 27 million Americans currently have osteoarthritis, and further dramatic increases are expected in the coming years as the population ages.

“Therefore, it is of great importance to identify modifiable risk factors for [osteoarthritis] progression,” Lu and colleagues wrote.

Milk plays an important role in the maintenance of bone health, and one study of a supplement containing milk micronutrients and another cross-sectional study of diet and osteoarthritis suggested benefits for milk.

“Knee [osteoarthritis] progression has been thought to involve multiple mechanisms besides cartilage loss, including changes in bone composition and shape, as well as proprioception, which might be subject to the influences of macro- and micronutrients in the diet,” the researchers explained.

To see the potential effects of drinking milk on osteoarthritis progression, the researchers analyzed outcomes for 2,148 participants in the Osteoarthritis Initiative who had radiographic evidence of the disease in at least one knee.

The study sample consisted of 3,064 knees that had Kellgren/Lawrence radiographic grade 2 or 3 osteoarthritis present.

Milk consumption was assessed on a food frequency questionnaire administered at baseline.

Participants’ mean age was 62. More than half were women.

Those who reported drinking milk regularly more often were white and nonsmokers.

The analysis adjusted for multiple covariates, including age, sex, education, employment, income, and social support.

For women, an increase of 10 glasses of milk each week over the 4-year study period was associated with a change in joint space width of 0.06 mm (P=0.020), the authors observed.

Different results were seen for other types of dairy products. For cheese, consumption of seven or more servings per week was associated with greater joint space width decrease when compared with no cheese consumption (P=0.003), while eating yogurt showed no effect.

Cheeses can contain high levels of saturated fats, which have been linked with the disease pathogenesis, the authors noted.

In a multivariate analysis, inverse associations were seen for osteoarthritis progression and higher levels of milk consumption per week among women (P for trend=0.008):

• Three or fewer glasses, HR 0.67 (95% CI 0.50-0.91)
• Four to six glasses, HR 0.71 (95% CI 0.50-1)
• Seven or more glasses, HR 0.56 (95% CI 0.38-0.81)

For men, risk was only reduced with consumption of seven or more glasses per week.

In a sensitivity analysis, women with the highest quartile of calcium intake had smaller decreases in joint space width compared with those in the lowest quartile. Increased calcium intake may contribute to the lower risk for progression, but the researchers noted that “the biologic mechanism for an effect of milk consumption on the radiographic progression of [osteoarthritis] remains unclear.”

In addition, women had lower calcium intake than men.

“If dietary calcium is a possible mediation factor to link between milk consumption and knee [osteoarthritis] progression, women may be more sensitive for the effect of calcium intake through milk than men,” they suggested.

A limitation of the study was its observational design, and causality cannot be assumed, they noted.

Another limitation of the study was a lack of information about whether milk was high-, low-, or fat-free, which could contribute to other related chronic conditions such as obesity.

“Replication of these novel findings” is warranted, the authors concluded.

In an accompanying editorial, Shivani Sahni, PhD, and Robert R. McLean, DSc, of Hebrew SeniorLife and Harvard Medical School, stated that the study doesn’t provide sufficient evidence for healthcare professionals to begin advising patients to drink milk to prevent progression of knee osteoarthritis.

“Clearly, further research is needed to clarify the biologic mechanism linking dairy foods and [osteoarthritis] and to replicate the findings of Lu and colleagues before considering their incorporation into current guidelines for the management of knee [osteoarthritis],” wrote Sahni and McLean.

Nonetheless, the editorialists commented, “the current research article is an important first step in that direction.”