The effects of a two‐year randomized, controlled trial of whey protein supplementation on bone structure, IGF‐1, and urinary calcium excretion in older postmenopausal women

Randomized controlled trial in healthy, ambulant postmenopausal women aged 70-80 years from metropolitan Perth, Western Australia. The whey protein arm included 101 participants at baseline, and the population had relatively high habitual protein intake.

The active intervention was a daily 250-mL oral skim milk-based whey protein drink, reconstituted from powder to provide 30 g protein, 600 mg calcium, and 3.2 kJ/mL. It was consumed before breakfast for 2 years and was matched to placebo for energy and calcium; the placebo contained 2.1 g protein.

Overall, 30 g/day whey protein increased serum IGF-1 but did not improve or worsen bone mass or strength over 2 years in this protein-replete population. Serum IGF-1 was higher in the protein group at year 1 by 7.3% ± 2.5% (p = .004) and at year 2 by 8.0% ± 3.3% (p = .016). There were no group-by-time interactions for hip bone variables or femoral neck engineering strength, and no between-group differences in changes in bone density or strength. Twenty-four-hour urinary calcium excretion increased over time in both groups at 1 year, and at 2 years it was 13.4% ± 7.3% higher than placebo in the protein group (p = .069).

Findings come from healthy older women with relatively high baseline protein intake, limiting generalizability to protein-deficient or other populations. The active-arm sample was modest, and the trial assessed surrogate bone and biochemical outcomes rather than fracture endpoints. The urinary calcium difference at 2 years was not statistically significant versus placebo (p = .069).