Context: Primary hyperparathyroidism (PHPT) and associated morbidity is comprehensively assessed in elderly females; however less is known of the disease in younger women.

Objective: To estimate the prevalence of mild disturbances in calcium homeostasis, that could be analogous with early PHPT, in a premenopausal population, and determine the potential presence of associated morbidity.

Design: Initial results from this longitudinal study from 2002 to 2004.

Setting: Population-based screening of s-calcium in conjunction with routine mammography.

Participants: Premenopausal women, 40 to 50 years of age (n=1900). Cases fulfilling previously evaluated biochemical criteria for PHPT (n=214) were matched to controls (n=214).

Main outcome measurements: All participants underwent investigation including; screening of parameters of calcium homeostasis, dual X-ray absorptiometry, and body mass index assessment, and filled out extensive health- and quality of life (SF-36) questionnaires. Participants were divided into four groups depending on the relation between s-calcium/iPTH. Statistical comparisons between cases and controls were performed, as well as among "the four groups" in order to evaluate morbidity.

Results: The prevalence of assumed mild PHPT i.e."inappropriate" iPTH value in relation to total s-calcium was estimated to be 5.1% (n=96). Women with mild disturbances in calcium homeostasis had statistically significant lower bone mineral density (BMD) in the proximal femur and femoral neck, higher BMI and lower scores for vitality and general health in the analysis of SF-36.

Conclusions: Mild disturbances in calcium homeostasis in premenopausal women were more prevalent than previously thought, and were associated with obesity, lower BMD and decreased quality of life.