Apple Women’s Health Study
The Apple Women’s Health Study is the first long-term research study of this scale and scope that aims to advance the understanding of menstrual cycles and their relationship to various health conditions.
Menstrual cycles today: how menstrual cycles vary by age, weight, race, and ethnicity – Data
More details about the information presented in the below tables are included in the study update on Menstrual cycles today: how menstrual cycles vary by age, weight, race, and ethnicity.
Table 1 Percentages of AWHS participants by age, race and ethnicity, and body mass index groups.
| Percentages (%) | Number of participants | |
| Age (years) | ||
| < 20 | 5.2 | 651 |
| 20-24 | 14.7 | 1853 |
| 25-29 | 17.2 | 2169 |
| 30-34 | 19.2 | 2424 |
| 35-39 | 18.3 | 2306 |
| 40-44 | 14.2 | 1787 |
| 45-49 | 8.4 | 1065 |
| ≥ 50 | 2.8 | 353 |
| Race and Ethnicity | ||
| White | 71.4 | 8996 |
| Black | 5.0 | 633 |
| Asian | 4.3 | 541 |
| Hispanic | 7.4 | 928 |
| Other | 2.2 | 280 |
| More Than One | 9.8 | 1230 |
| Body Mass Index (kg/m2) | ||
| < 18.5 | 2.6 | 330 |
| 18.5 – 24.9 | 36.8 | 4636 |
| 25 – 29.9 | 25.9 | 3263 |
| 30 – 34.9 | 16.8 | 2112 |
| 35 – 39.9 | 9.7 | 1223 |
| ≥ 40 | 8.3 | 1044 |
Table 1 presents the percentage and number of AWHS participants in each age, race and ethnicity, and body mass index groups. For race and ethnicity, the White group included participants who only selected ‘White, non-Hispanic’ in the Common Demographics survey; the Black group included participants who only selected ‘Black or African American or African’ in the survey; the Asian group included participants who only selected ‘Asian’; the Hispanic group included participants who only selected ‘Hispanic, Latino, Spanish and/or other Hispanic’; the Other group included participants who selected answers other than those mentioned previously (‘American Indian or Alaska Native,’ ‘Middle Eastern or North African’, ‘Native Hawaiian or Pacific Islander,’ or ‘none of these categories can fully describe me’); the More Than One group included participants who selected more than one race and ethnicity options in the survey. Body mass index was calculated from the self-reported height and weight in the Common Demographics survey. These BMI categories were defined based on the adult BMI classification from the Center of Disease Control and Prevention.
Table 2 Average menstrual cycle length and variability in different age groups of AWHS
| Age (years) | Average menstrual cycle length | Cycle length variability |
| < 20 | 30.37 days | 5.33 days |
| 20-24 | 30.17 days | 5.07 days |
| 25-29 | 29.86 days | 4.70 days |
| 30-34 | 29.31 days | 4.28 days |
| 35-39 | 28.74 days | 3.79 days |
| 40-44 | 28.25 days | 3.99 days |
| 45-49 | 28.41 days | 5.42 days |
| ≥ 50 | 30.76 days | 11.19 days |
Table 2 presents the average menstrual cycle length and variability for AWHS participants in different age groups. Age was determined by the self-reported birth year and the year each cycle was tracked in the Health app. The cycle length variability was calculated as the average standard deviation of menstrual cycle length for an individual in that age group, meaning that 70% of the menstrual cycles of that individual are expected to vary within that range around the average.
Table 3 Average menstrual cycle length and variability in different race and ethnicity groups of AWHS
| Race and ethnicity | Average menstrual cycle length | Cycle length variability |
| White | 29.12 days | 4.81 days |
| Black | 28.88 days | 4.67 days |
| Asian | 30.69 days | 5.04 days |
| Hispanic | 29.85 days | 5.09 days |
| Other | 29.30 days | 4.63 days |
| More Than One | 29.24 days | 4.58 days |
Table 3 presents the average menstrual cycle length and variability of AWHS participants in different race and ethnicity groups. The White group included participants who only selected ‘White, non-Hispanic’ in the Common Demographics survey; the Black group included participants who only selected ‘Black or African American or African’ in the survey; the Asian group included participants who only selected ‘Asian’; the Hispanic group included participants who only selected ‘Hispanic, Latino, Spanish and/or other Hispanic’; the Other group included participants who selected answers other than those mentioned previously (‘American Indian or Alaska Native,’ ‘Middle Eastern or North African’, ‘Native Hawaiian or Pacific Islander,’ or ‘none of these categories can fully describe me’); the More Than One group included participants who selected more than one race and ethnicity options in the survey. The cycle length variability was calculated as the average standard deviation of menstrual cycle length for an individual in that age group, meaning that 70% of the menstrual cycles of that individual are expected to vary within that range around the average.
Table 4 Average menstrual cycle length and variability in different body mass index (BMI) groups of AWHS
| Body mass index (kg/m2) | Average menstrual cycle length | Cycle length variability |
| < 18.5 | 28.93 days | 4.89 days |
| 18.5 – 24.9 | 28.90 days | 4.57 days |
| 25 – 29.9 | 29.16 days | 4.82 days |
| 30 – 34.9 | 29.44 days | 5.03 days |
| 35 – 39.9 | 29.65 days | 4.77 days |
| ≥ 40 | 30.44 days | 5.43 days |
Table 4 presents the average menstrual cycle length and variability of AWHS participants in different BMI groups. BMI was calculated using the self-reported height and weight in the Common Demographics survey. These BMI categories were defined based on the adult BMI classification from the Center of Disease Control and Prevention. The cycle length variability was calculated as the average standard deviation of menstrual cycle length for an individual in that age group, meaning that 70% of the menstrual cycles of that individual are expected to vary within that range around the average.