Effects of dairy product intake and home-based resistance exercise on the physical function in Japanese community-dwelling older adults: results of a real-world randomized controlled trial

Purpose Although the combination of dairy product intake and resistance training has shown benefits for muscle health in older adults, most intervention studies have been conducted under highly controlled conditions, limiting their applicability to real-world settings. Methods We conducted a 12-week pragmatic, open-label randomized controlled trial involving community-dwelling Japanese older adults. Fifty-four adults aged ≥ 65 years were assigned to either a dairy product intake plus home-based resistance training group (milk and exercise; ME) or a home-based resistance training only group (E). The dairy intervention targeted an increase equivalent to approximately 10–15 g of dairy-derived protein per day within habitual meals. Both groups were instructed to perform home-based resistance training at least three days per week. The physical function, including upper and lower limb strength, handgrip strength, gait speed, and body composition, was assessed before and after the intervention. Exploratory subgroup analyses were conducted according to baseline dairy consumption and skeletal muscle mass. Results Fifty-one participants (mean age, 78.2 ± 6.9 years; BMI, 22.9 ± 3.2 kg/m²) completed the study (retention rate: 94.4%). Adherence to milk supplement consumption was exceptionally high (median 7.00 times/week, IQR 7.00–7.00 times/week). The median frequencies of milk and dairy product intakes were 6.83 (IQR 5.60–7.00) and 6.83 (IQR 6.17–6.94) times/week, respectively. Resistance exercise adherence was comparable between the ME and E groups (3.13 [2.81–3.65] vs. 3.25 [2.71–3.96] times/week; p = 0.940). No significant differences were observed between the groups in terms of muscle strength, physical function, or body composition. However, some functional outcomes improved over time in both groups. In exploratory subgroup analyses, participants with lower habitual dairy consumption at baseline showed improvements in upper and lower limb strength only in the ME group. Conclusions Adding modest dairy product intake to home-based resistance training did not provide additional overall benefits compared to exercise alone. However, exploratory findings suggest that baseline dairy consumption may influence the responsiveness of older adults to combined nutrition and exercise interventions. Trial registration Registration number UMIN000052127 Date of registration 2023/09/08 URL https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000059497.