Fermented dairy and muscle strength in older adults show no consistent link across two Irish cohorts

Sarcopenia, the age-related loss of muscle mass, strength, and performance, drives frailty and loss of independence. Older muscle also responds less to dietary protein, a problem called anabolic resistance. Fermented dairy foods such as yogurt, cheese, and cottage cheese are often promoted for muscle health because they supply high-quality protein and may act through the gut-muscle axis. Most of that case rests on mechanistic and preclinical reasoning rather than population or trial data, which is the gap this study addressed.

The researchers ran cross-sectional analyses in two independent cohorts. NICOLA (Wave 1, 2013-2016) included 2,791 adults after excluding 101 with implausible energy intakes; mean age was 64. Intake came from the EPIC-Norfolk food frequency questionnaire, expressed in grams per day (mean 54 g/day; tertile means 7, 33, and 123 g/day) and analyzed per 50 g/day and by tertile. TILDA (Wave 3) included 3,999 adults, mean age 66, with exposure derived from yogurt and cheese frequency on a 52-item questionnaire. Outcomes were grip strength, low grip strength (EWGSOP2 cutoffs: under 27 kg for men, under 16 kg for women), Timed Up-and-Go, activities of daily living limitations, and a 30-item frailty index. Four sequential models adjusted progressively for age, sex, BMI, physical activity, socioeconomic factors, smoking, and alcohol.

In NICOLA, the crude analysis showed an inverse association with grip strength (β = -0.66 kg per 50 g/day; p<0.001). That disappeared after adjusting for age and sex (β = 0.02) and stayed null in the fully adjusted model (β = 0.25; 95% CI -0.69, 1.19; p=0.597). The likely reason is confounding by sex: 61% of the highest-intake tertile were women versus 39% men, and women have lower absolute grip strength. Frailty index, Timed Up-and-Go, and daily-living limitations were also unrelated to intake, and odds ratios for low grip strength and frailty were near 1 with intervals crossing 1.

Descriptively, the highest-intake NICOLA tertile looked healthier: 20% were frail versus 27% in the lowest tertile (p=0.038), Timed Up-and-Go was about 15 versus 16 seconds, and 9.7% versus 11.8% had daily-living limitations. These people also reported higher energy and protein intake, more physical activity, and more education, a typical healthy-consumer pattern. Those differences did not survive confounder adjustment. Tertile analysis showed lower crude grip strength in the top group (β = -1.93; p=0.001), and no dose-response relationships emerged after adjustment.

TILDA told a similar story. Crude grip strength was inversely associated with intake (β = -0.86; p<0.001) but fell to -0.05 after age and sex adjustment. Frailty, Timed Up-and-Go, and daily-living limitations were null in adjusted models. The one nominal signal was higher odds of low grip strength in the highest versus lowest tertile of fermented dairy intake (OR 2.71; 95% CI 1.12-6.88; p=0.030). Analysis of individual foods showed this was driven by yogurt, and it was attenuated after covariate adjustment. In continuous modeling, the fully adjusted odds ratio was 1.51 (0.97-2.30; p=0.056).

Overall, fermented dairy intake was not consistently linked to physical function in either cohort. Caveats include the cross-sectional design, which cannot establish causality or direction, and self-reported questionnaires with different exposure definitions across cohorts. TILDA also lacked energy, protein, and deprivation data. Few participants had low grip strength (5.8% in NICOLA), which makes the wide intervals fragile. The study neither supports nor refutes a muscle benefit, and longitudinal and interventional studies are needed.