Urinary equol concentration, body composition, and lifestyle factors were associated with bone mass in young women

Osteoporosis, a disease characterized by decreased bone strength and increased risk of fracture, represents a significant health concern in older adults. Primary osteoporosis prevention requires increasing bone mass (BM) to its peak at a young age. The estrogen-like effect of equol has been reported to suppress bone loss in postmenopausal women. This study aimed to investigate the relationship between BM and the urinary equol concentration, body mass, skeletal muscle mass, exercise habits, and menstrual abnormalities in younger women. Of a total of 395 female university students recruited, the final analysis included 275 participants after excluding those taking hormonal agents, those who did not undergo an equol test, and those who did not respond to the questionnaire. The mean age of the 275 participants was 20.1 years (± 1.1). BM was measured in the right calcaneus using an ultrasonic bone densitometer. BM was assessed using the osteo-sonoassessment index of the right calcaneus. Body composition was measured via the bioelectrical impedance method, using a multifrequency body composition analyzer. Hormone use, menstrual cycle, current exercise habits, and daily soy intake were assessed using self-administered questionnaires. Urinary equol concentration was measured using a Soy-Check system. Multiple regression analysis, using the forced-entry method, was performed with BM as the objective variable; and age, body mass index, skeletal muscle mass index, soy intake, exercise habits, menstrual cycle, and urinary equol concentration as the explanatory variables. In our multiple regression analysis with osteo-sonoassessment index as the objective variable, the significantly associated factors were determined to be urinary equol concentration (β = 0.11, p < 0.05), skeletal muscle mass index (β = 0.29, p < 0.01), and current exercise habits (β = 0.31, p < 0.01). By contrast, age, body mass index, soy intake, and menstrual cycle were not found to be significantly associated with osteo-sonoassessment index (p > 0.05). Young women with higher urinary equol concentration, exercise habits, and skeletal muscle mass index had higher levels of BM. The acquisition of maximal BM at a young age is protective against osteoporosis; therefore, increased urinary equol concentration at a young age may be associated with better bone health and could potentially contribute to osteoporosis prevention.