Genetically defined adult-type hypolactasia and self-reported lactose intolerance as risk factors of osteoporosis in Finnish postmenopausal women

Objective: To study the relationships of molecularly defined lactose malabsorption (LM) and self-reported lactose intolerance (LI) to bone mineral density (BMD) and fractures among Finnish postmenopausal women. Design: A cross-sectional study of two cohorts. Setting: Helsinki University Central Hospital. Subjects: One cohort was population-based and comprised 453 women, aged 62 - 78 ( mean 69) y. Another comprised 52 women, aged 69 - 85 ( mean 75) y, with osteoporotic fractures and 59 control women, aged 69 - 83 ( mean 74) y, without osteoporosis. Methods: A single nucleotide polymorphism of the lactase (LCT) gene at chromosome 2q21 - 22 was studied. It shows complete association with intestinal disaccharidase activity, with the genotype CC-13910 meaning adult-type hypolactasia ( primary LM) and the genotypes CT-13 910 and TT-13 910 lactose absorption. BMD of the heel was measured by dual-energy X-ray absorptiometry (DXA). Results: In the population-based cohort, 16.0% of women had self-reported LI but only 15.3% of them had the CC (- 13 910) genotype. Calcium intake from dairy products (P = 0.10) and BMD, adjusted for age, weight, height, exercise, smoking, and estrogen use (P = 0.71) were similar for the genotypes. Women with self-reported LI had reduced calcium intake from dairy products (P<0.0001) but they were more frequent users of calcium supplements than lactose-tolerants (P<0.0001). Adjusted BMD was similar for lactose intolerant and tolerant women (P = 0.60). Of 104 women with previous fracture in the population-based cohort, 13.5% had the CC (- 13 910) genotype, which did not differ from the prevalence of 19.3% among 347 women without fractures ( P = 0.29). The frequency of the CC (- 13 910) genotype (23.1%) for 52 women with established osteoporosis was similar as for 59 control women (15.3%) (P = 0.19). Conclusion: Molecularly defined LM and self-reported LI are not risk factors for osteoporosis, if calcium intake from diet and/or supplements remains sufficient. Our study confirms the poor correlation between self-reported LI and LM established by different techniques.