Calcium, Vitamin D, and Phosphorus Levels and Bone Health in Adults with Lactose Intolerance: A Systematic Review.

CONTEXT: Lactose intolerance (LI) is a common condition characterized by lactase deficiency and impaired digestion of lactose. Dairy avoidance among affected individuals can reduce intakes of calcium, vitamin D, and phosphorus, with potential implications for bone health. Therefore, this review aimed to assess the effects of LI on calcium, vitamin D and phosphorus status, as well as related bone health in adults. OBJECTIVE: This systematic review synthesizes evidence regarding implications for bone health reported in observational studies on calcium, vitamin D, and phosphorus status in adults with LI and dairy avoidance. DATA SOURCES: PubMed, Web of Science, Scopus, and CINAHL were searched for studies from 1980 to 2024. The strategy followed the population-intervention-comparison-outcome framework and used MeSH terms with Boolean operators. Eligible designs were observational; most were cross-sectional studies and included adults (aged ≥18 years) with LI. DATA EXTRACTION: Data were extracted on study characteristics, population demographics, diagnostic methods, assessment of micronutrient status, and bone outcomes. Risk of bias was assessed using the Newcastle-Ottawa Scale, adapted for cross-sectional designs. DATA ANALYSIS: A narrative synthesis following the Synthesis Without Meta-analysis (SWiM) guidelines was used to compare nutritional and bone outcomes between lactose-intolerant and lactose-tolerant groups. Thirteen studies were included. Overall, study quality was mostly good or satisfactory, with few studies rated as unsatisfactory or fair. For serum calcium and phosphorus, studies generally did not demonstrate differences by LI status. Evidence on vitamin D was limited to 3 studies with heterogenous results; therefore, we cannot conclude that vitamin D status is unaffected. Conversely, LI was generally associated with significantly reduced calcium intake. Bone outcomes were inconsistent. CONCLUSIONS: Given inconsistent evidence across studies, chronically low calcium intake in LI may be associated with, but not definitively causal for, adverse bone outcomes. Our findings support ensuring sufficient calcium intake and highlighting the need for prospective studies. SYSTEMATIC REVIEW REGISTRATION: PROSPERO registration No. [CRD42024607063].