Coffee only looked bad for older women's bones above five cups a day

Bone density falls after the menopause, and coffee and tea are the two drinks older women consume most often, so any effect on the skeleton would matter at population scale. The evidence has stayed inconclusive for years, partly because most studies measured drinking habits once and bone density once, which cannot capture how either changes over time. Caffeine has long been suspected of interfering with calcium, while tea contains compounds sometimes credited with the opposite effect. The useful question is whether repeated measurement of both the drinks and the bones over a decade shows anything consistent.

The analysis used the Study of Osteoporotic Fractures, a prospective cohort of 9704 women aged 65 years and over. Coffee and tea intake were reported by the women themselves on questionnaires at visits 2, 4, 5 and 6, spanning approximately 10 years, and bone mineral density at the femoral neck and total hip was measured repeatedly by dual-energy X-ray absorptiometry. The researchers fitted linear mixed-effects models with random intercepts, adjusting for demographics, physical activity, other health conditions and medication use. They also tested for non-linear patterns using natural splines and looked for differences between subgroups by adding interaction terms.

Tea consumption was associated with higher total hip bone density, with least squares means of 0.718 versus 0.715 g/cm2, a mean difference of 0.003 (p = 0.026). Coffee showed no significant overall association with either femoral neck or total hip density. The spline analysis suggested that drinking more than five cups of coffee a day may be linked with lower density, a pattern the main model missed. Two interactions reached significance: between coffee and alcohol intake (p = 0.0147), with coffee negatively associated with femoral neck density in women drinking more alcohol, and between tea and body mass index (p = 0.0175), with tea appearing more favourable in women with obesity.

This adds repeated measurement of both exposure and outcome to a literature built largely on single snapshots, which is a genuine methodological step up. It broadly reassures on ordinary coffee drinking while keeping alive the idea that very high intakes, or coffee combined with more alcohol, might sit differently. The tea finding points the same direction as earlier suggestions of a modest benefit, but the size of the difference here is tiny and the intake was self-reported. Because the women were not assigned their drinks, unmeasured differences in diet, sunlight, calcium or frailty could still be doing some of the work, and no fracture outcomes were reported.

For a woman past 65 with a normal coffee habit, this study offers no signal that her bones are suffering for it. The tea association is real in the statistics but so small that no one should reframe tea as a bone treatment. The more interesting hints are conditional: heavier coffee intakes, and coffee alongside more alcohol, are where the less favourable numbers showed up. As this tracked habits rather than testing them, it is a reason to be curious rather than to change what is in the cup.