2.1 Background data
A total of 5,852 women were surveyed and completed the questionnaire, of whom 4,426 were effectively surveyed, with a valid completion rate of 75.6%. The age range was 32-75 (59.3 ± 6.98) years old. All participants were menopausal. A total of 1426 women were excluded, including those who had surgical removal of ovaries or uterus, those with endocrine diseases (e.g., hyperthyroidism, diabetes, polycystic ovary syndrome), and those who received hormone therapy (≥3 months) and other potentially interfering medication. Finally, 4426 naturally menopausal women under physiological conditions were analyzed. The maximum age of menopause was 65 years, and the minimum age of menopause was 32 years, with a mean of 49.49 ± 3.67 years. Based on the average age of menopause, we divided the survey sample into the younger menopause group (<45 years old), the normal menopause group (45-55 years old), and the older menopause group (>55 years old).
2.2 Natural menopause age
The mean age of onset of natural menopause was 49.49 ± 3.67 years. Among the natural menopause population, there were 327 cases (7.4%) of early menopause (<45 years), 3927 cases (88.7%) of normal menopause (45-55 years), and 172 (3.9%) cases of late menopause (>55 years).
2.3 Factors that influence menopausal age
The distribution of early, normal, and late menopause and the possible influencing factors are shown in Table 1. Logistic regression analysis to determine which factors had a statistically significant influence on the age of menopause is shown in Table 2. Logistic regression analysis of relevant influencing factors of menopausal age is shown in Table 3.
The results of the chi-square test (Table 1) revealed that marital status, frequency of drinking tea, frequency of smoking, alcohol consumption, frequency of eating fruits, taking dietary supplements, sleep quality, and contraceptive method were statistically significant among the three groups, while the proportion of vegetarian habits had no significant difference.
Logistic regression analysis (Table 2) shows that body weight, age of menarche, marital status, tea drinking (often and daily), taking supplements, oral contraceptive use, and safe period contraception methods significantly influenced menopause age. However, fertility times, occasionally drinking tea, drinking wine, eating fruits, drinking milk, condom use, and ligation and intrauterine ring contraceptive methods showed no significant difference.
The results showed that for every increase in the number of pregnancies, the age of menopause was advanced by 0.71 years; an increase of 1 kg in body weight increased the age of menopause by 0.018 years; and the age of menopause of married women was delayed by 2.587 years compared with those unmarried. Compared with people who never drank tea, occasional tea drinking had little effect on the age of menopause. The menopause age of people who drink tea frequently was delayed by 0.863 years, while the menopause age of people who drink tea daily was delayed by 0.914 years. Compared with people who never take the donkey-hide gelatin supplements, the age of menopause in those who take supplements occasionally was delayed by 0.418 years, the menopause age of people who take regular supplements was delayed by 0.806 years, and the menopause age of people who take daily supplements was delayed by 1.548 years. Compared with people who had never used contraception, the age of menopause was 0.404 years earlier for those who use oral contraceptives and 0.603 years earlier for those who adopted safe period contraception. Logistic regression analysis demonstrated that body weight and age of menarche were predictive for menopausal age, and the fertility times are not correlated with menopausal age (Table 3).