Assessing the Impact of Dietary Calcium–Magnesium Ratio on Calciotrophic Hormones and Body Composition Using Validated Food Frequency Questionnaires

Background: Calcium (Ca) and magnesium (Mg) are essential micronutrients integral to metabolic processes and cardiovascular health. Emerging evidence suggests that the dietary Ca:Mg ratio may influence chronic disease risk, yet variability in this ratio across diverse demographic groups and its relationship to body composition and vitamin D status remain unclear. Methods: Dietary intakes of Ca and Mg were assessed using validated Food Frequency Questionnaires (FFQs) and body composition was quantified via Dual-energy X-ray Absorptiometry (DXA) scans. Relationships between dietary Ca:Mg ratios and demographics, body composition parameters (lean and fat mass), and vitamin D and parathyroid hormone (PTH) levels were examined statistically using SPSS ver. 29.0 and R ver. 4.5.1 (2025) employing Kruskal–Wallis, regression, and moderated mediation analyses. Results: We examined 155 healthy adults with a mean age of 36.6 ± 12.5 years. Only 16.8% had adequate intakes of Mg compared with 45.8% who had adequate dietary Ca intakes. Significant differences in the Ca:Mg ratio were observed across racial groups (p = 0.023) and age groups (p = 0.017). South Asian Indians exhibited the highest median Ca:Mg ratio (4.83), whereas African Americans exhibited the lowest (2.67). Interestingly, our moderated mediation analysis indicated that African Americans were the most sensitive to the impact of PTH changes on the balance of Ca:Mg (indirect effect = −0.762, 95% CI [−1.298, −0.234]), indicating that even slight shifts in their Ca:Mg balances cause significant elevation in the PTH, which, in turn, leads to lowering of their vitamin D levels. Young adults (ages 18–29) had the highest median Ca:Mg ratio (4.73). No statistically significant differences were detected based on Gender (p = 0.425 and BMI (p = 0.744) on Ca:Mg ratios. Additionally, dietary Ca:Mg ratios were positively associated with sPTH in males (r = 0.203, p < 0.05), but not with body composition. Conclusion: Important variations in dietary Ca:Mg ratios exist across racial and age demographics, notably among young adults, and specific ethnic groups exhibited elevated ratios. Tailored nutritional interventions may be necessary for these populations to optimize Ca:Mg balance and support metabolic and cardiovascular health outcomes in these populations.