Resistance training 3X weekly in Type 2 Diabetes – 12 weeks - tiny RCT

Combined Effects of Combined Resistance Exercise and Vitamin D Supplementation on Cardiometabolic Profiles and Functional Capacities in Elderly Women with Type 2 Diabetes

Metabolites, 19 August 2026, https://doi.org/10.3390/metabo16080593

Hyoung-Jun Kim, Deok-Su Yoo, Man-Gyoon Lee

Observation: 2000 IU for 12 weeks was too little to help. A high loading dose initially might have done better

Summary by Claude - August, 2026

Twelve weeks of supervised progressive resistance training (3X weekly) produced large strength, balance, and lipid improvements in 52 elderly Korean women (aged 65-80) with Type 2 Diabetes and 25(OH)D below 20 ng/mL. Adding 2000 IU/day of cholecalciferol added little on top of the exercise, and vitamin D by itself added almost nothing.

This was a 2X2 factorial RCT with four small groups: Exercise+Vitamin D (n=15), Exercise+Placebo (n=13), Vitamin D only (n=11), Control (n=13). Supplementation worked chemically — 25(OH)D rose from about 11 to 27 ng/mL and PTH fell — yet the Vitamin D-only group showed no significant change in HbA1c, fasting glucose, insulin, HOMA-IR, strength, or balance. Essentially every clear benefit tracked with the exercise factor.

The paper's headline claim of "enhanced combined improvements" is not supported by its own statistics. The formal exercise X vitamin D interaction was non-significant for HbA1c, glucose, insulin, HOMA-IR, calcitonin, all four lipid measures, and every strength measure. The single significant interaction — functional reach — actually favored Exercise+Placebo (+4.46 cm vs +2.47 cm). The impressive "combined" figures in the abstract are within-group before/after changes in a 15-person arm, not evidence that the two treatments work together.

What this does not show / limitations: synergy was not statistically demonstrated. HbA1c fell only 0.13% from an almost-normal 6.61% baseline. The groups were far too small to detect an interaction. Much of the apparent Ex+VitD advantage came from deterioration in the 13 controls (insulin rose 4.69 to 9.95 µU/mL). The achieved 25(OH)D of 27 ng/mL remains below what many consider adequate — the authors list "the modest vitamin D dose (2000 IU/day)" among their own limitations. Data were collected in 2013 but published in 2026.

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