The evidence that insufficient protein intake increases the risk of bone fractures in older adults is reasonably convincing and supported by multiple types of research, including a large randomised trial. Additional dairy raised protein intake in frail older adults to around 1.1 grams per kilogram of body weight per day and reduced the number of hip fractures by nearly half. Guidelines for both postmenopausal women and people using corticosteroids now explicitly identify adequate protein as a basic measure. Practical advice: keep protein intake at a minimum of 1.0 to 1.2 grams per kilogram per day, combined with calcium and vitamin D.
Eating too little protein increases the risk of bone fractures at older age through two mechanisms at once. Protein deficiency not only undermines bone mass itself, but also weakens muscles. Weaker muscles mean more falls, and every fall in someone with fragile bones is more likely to result in a fracture. In addition, adequate protein intake stimulates the production of IGF-1, a growth factor that plays an important role in bone formation. A low IGF-1 level is an independent risk factor for hip fracture1.
The strongest direct evidence comes from a large randomised controlled trial involving 7195 nursing home residents with a mean age of 86 years in Australia. Residents who received additional dairy products daily (milk, yoghurt, cheese) increased their calcium intake from 700 to 1142 mg per day and their protein intake from 0.9 to 1.1 grams per kilogram of body weight. The result: 46% fewer hip fractures, 33% fewer fractures overall and 11% fewer falls. Mortality was unchanged2. These are large reductions in a vulnerable population.
Protein does not act on bone health in isolation, but as part of a trio: protein, calcium and vitamin D complement one another. In older adults who received protein supplementation after a hip fracture, IGF-1 levels rose, bone mineral density at the hip was preserved and rehabilitation time in hospital was significantly shorter. These benefits occurred when vitamin D and calcium intake were also sufficient. If any one of the three was lacking, the effect was less pronounced1. Adequate protein also improves the absorption of calcium in the gut, which further strengthens the chain from muscle to bone3.
People following a vegan diet face an increased risk of bone fractures based on multiple large prospective cohort studies. Vegetarians fall in between, with a smaller but still elevated risk. Lower protein intake is one of the suspected causal factors, alongside lower calcium and vitamin D and a lower body weight. This is observational research, so direct causality has not been definitively established. Supplementation with vitamin D and calcium, combined with a conscious choice of protein-rich plant foods (legumes, nuts, soy products), appears able to partially offset the risk4.
In practice, adequate protein intake now features explicitly in clinical guidelines. The position statement of the North American Menopause Society (NAMS, 2021) recommends that all postmenopausal women consume sufficient protein, calcium and vitamin D as a basic measure against bone loss and fractures, before medication is even considered5. European guidelines go one step further: anyone using corticosteroids (such as prednisone) for three months or longer must maintain adequate protein intake as a mandatory part of treatment, alongside calcium and vitamin D6. Specific recommendations for older adults generally range from 1.0 to 1.2 grams of protein per kilogram of body weight per day, with higher amounts following a fracture or during rehabilitation.
Seven claims based on seven PMIDs: one large RCT (n=7195), multiple prospective cohort studies, two guideline publications (NAMS 2021, ECTS 2024), one narrative review and one smaller intervention study/review. The RCT provides the strongest direct evidence. The observational data in vegans are associative.