Women over 70 are often advised by their physicians to take calcium supplements. Osteoporosis affects approximately one in five women in this age group, and calcium, often combined with vitamin D, has long served as a foundational strategy for fracture prevention. Millions of women adhere to this regimen daily.
But for the past decade, a quiet concern has shadowed that recommendation. Two observational studies suggested a troubling possibility: that calcium supplements might be linked to higher dementia risk. One 2016 Swedish study reported that women taking calcium supplements had up to nearly seven times higher odds of developing dementia, particularly those with a history of cerebrovascular disease. Another study found that users of calcium supplements had greater brain lesion volumes on MRI scans.
These findings raised concerns among both patients and clinicians, prompting questions about whether women must choose between bone health and cognitive well-being.
A landmark study published in The Lancet Regional Health – Western Pacific in 2025 offers the most rigorous evidence to date and provides reassuring conclusions.
Study Design and Objectives
The research comes from the Perth Longitudinal Study of Aging Women (PLSAW), based in Western Australia. It is a post-hoc analysis of the Calcium Intake Fracture Outcome Study (CAIFOS), a large, double-blind, placebo-controlled randomized clinical trial originally designed to test whether calcium supplements reduced fracture risk.
Key aspects of the study include the following:
Participants included 1,460 community-dwelling Australian women aged 70 years and older, all of whom were dementia-free at baseline. The cohort was randomly assigned to receive either calcium supplements (n = 730) or a placebo (n = 730), with both participants and researchers blinded to group allocation.
The intervention group received 1,200 mg of calcium carbonate daily (administered as 600 mg twice daily with meals) for 5 years, from 1998 to 2003.
Following the 5-year intervention period, participants’ health outcomes were monitored for an additional 9.5 years using linked hospital records and death certificates, for a total follow-up period of 14.5 years.
What counted as dementia: Any dementia-related hospitalization or death recorded in the Western Australian Data Linkage System, including Alzheimer’s disease, vascular dementia, and unspecified dementias tracked using internationally standardized diagnostic codes.
This study was a large-scale, rigorously controlled randomized controlled trial with one of the longest follow-up periods in this research area.
Study Findings: No Association Between Calcium Supplementation and Dementia
Over 14.5 years, 269 women (18.4%) experienced a dementia event, 243 had dementia-related hospitalizations, and 114 died from dementia-related causes. The average age at which dementia events occurred was 85.3 years.
The primary finding was that there was no statistically significant difference in dementia outcomes between the calcium and placebo groups.
Women assigned to calcium supplementation had a hazard ratio of 0.90 for dementia events compared to placebo, indicating a non-significant trend toward lower risk in the supplement group. Comparable results were observed for dementia-related hospitalizations (hazard ratio 0.89) and dementia-related deaths (hazard ratio 0.78).
These findings did not change when researchers adjusted for a comprehensive range of potential confounders, including age, body mass index, APOE genotype (the strongest known genetic risk factor for Alzheimer’s), blood pressure, diabetes, statin use, aspirin use, smoking, physical activity, alcohol intake, dietary calcium intake, socioeconomic status, and cardiovascular disease.
Analysis of the subgroup with pre-existing vascular disease, previously identified as potentially vulnerable in observational studies, also revealed no increased risk of dementia associated with calcium supplementation.
Why Previous Studies Got Wrong
It is important to understand why earlier studies raised concerns and why this trial offers more robust evidence.
The 2016 study that raised concern was observational. It compared women who were already taking calcium supplements with those who were not, without random assignment. This design introduces confounding by indication, as women prescribed calcium supplements often have osteoporosis, previous fractures, or lower bone density conditions associated with poorer overall health and increased dementia risk. Consequently, supplement use may reflect underlying vulnerability rather than causation.
The PLSAW study mitigates this issue by randomizing participants to calcium or placebo, ensuring equivalent baseline health profiles across groups. Therefore, any observed differences in dementia outcomes can be attributed to the intervention rather than pre-existing health disparities. Hodological advantages of this study over the earlier observational work include a longer follow-up period (14.5 years versus 5 years), a much larger sample size with far more dementia events for statistical analysis, direct provision of supplements with tracked adherence rather than reliance on pharmacy dispensing records, and the use of both hospital morbidity data and death records to identify dementia cases.
What This Means for Women Taking Calcium
The clinical implications of these findings are both significant and clear.
For women aged 70 and older who take calcium supplements for bone health, this study offers the most robust evidence to date that five years of calcium supplementation at 1,200 mg per day does not increase long-term dementia risk, even with nearly 15 years of follow-up.
As the authors state plainly: “Findings do not support concerns that calcium supplementation increases long-term risk of dementia.”
These findings provide reassurance for patients who may have discontinued or hesitated to initiate calcium supplementation due to concerns about cognitive health. They also assist clinicians in balancing the benefits of bone health with potential cognitive risks.
Additionally, the study found no significant difference in cognitive test scores between the calcium and placebo groups at the conclusion of the five-year trial, further supporting the primary findings.
Important Nuances to Understand
While this study is methodologically robust, it is important to acknowledge its limitations.
The participants were older White Australian women. Whether the same findings apply to men, to younger women, to different ethnicities, or to women with very different dietary calcium intakes (the women in this study were already consuming around 960 mg per day from food alone). The intervention period was limited to five years, and calcium supplement use beyond the trial was neither tracked nor controlled. The effects of very long-term supplementation, such as over a decade, remain unknown. Applications remain unknown.
The study evaluated all-cause dementia as a single category and did not examine whether calcium might affect specific dementia subtypes differently.
These limitations do not undermine the central finding but rather delineate the scope of the current evidence and highlight areas for future research.
Conclusion
For decades, recommendations regarding calcium supplementation for bone health have been complicated by concerns about cognitive safety, primarily based on small observational studies with significant methodological limitations.
This study, which included 1,460 women randomly assigned and followed for 14.5 years with comprehensive outcome tracking, represents the highest-quality evidence currently available. The findings indicate that calcium supplements taken at 1,200 mg per day for five years do not increase the long-term risk of dementia in older women.