Confirmation of Biological Parameter regarding Estimating Age at Menarche

An approach from change curve of BMI and Rohrer index with age

Abstract

There are very few reports on the changes with age in BMI and Rohrer index, and little discussion on the relationship between the age-related changes in these two indices and the age at menarche. In the present study, we applied the wavelet interpolation method (WIM) to changes with age in BMI and the Rohrer index between the first year of elementary school and the third year of high school. We then analyzed the age-distance curve of BMI and the Rohrer index. From the results we identified the age at maximum peak velocity of BMI and the lowest point on the trough of the Rohrer index. By verifying the relationship with age at menarche, we investigated whether the MPV of BMI and the lowest trough point of the Rohrer index were valid as biological parameters. The subjects were 102 university students at a women's university in the Tokai region of Japan, who completed a questionnaire regarding age at menarche and level of exercise. Longitudinal growth information for height and weight were obtained from school health check records from the first year of elementary school until the third year of high school (from 1987 to 1998). BMI and the Rohrer index were calculated from height and weight values for these years, and the WIM was applied to the distances of the BMI and Rohrer index in these school years. Curves showing the changes with age in BMI and the Rohrer index were drawn with the WIM, and the age at MPV of BMI was identified from the peak velocity curve, which for BMI is the differential curve. With regard to the Rohrer index, the lowest trough point was identified from the age-distance curve. It was seen that the age at menarche and the age at MPV of BMI were nearly the same. It was also indicated that the interval between the age at MPV of BMI and the age at menarche was nearly 0. The mean difference between the lowest trough point of the Rohrer index and the age at menarche was 0.7 ± 1.00, with menarche occurring at about 0.7 years before the lowest trough point of the Rohrer index. Therefore, we conjecture that these two indices are valid biological parameters, with age at MPV of BMI indicating the critical period for age of menarche, and the lowest trough point of the Rohrer index the inflection point of internal body density.