Table 1.
Characteristics of Iowa Women’s Health Study participants at their reported drinking water source > 10 years, by nitrate-nitrogen (NO3-N) levels in public water supplies (PWS) and private well use.
| Public water supplies (N=15,910) | Private wells (N=5035) | |||||
|---|---|---|---|---|---|---|
| Mean NO3-Na (mg/L) | ||||||
| Characteristic | <0.47 | 0.47-1.08 | 1.09-2.97 | 2.98-5.69 | >5.69 | |
| n | 4064 | 3913 | 4211 | 2912 | 810 | 5035 |
| Mean length of follow-up, years | 21.2 | 21.0 | 21.1 | 21.2 | 20.9 | 21.9 |
| Mean age at baseline, years | 61.7 | 61.6 | 61.6 | 61.6 | 61.5 | 61.2 |
| White race, % | 99.5 | 99.2 | 99.2 | 98.6 | 99.3 | 99.6 |
| PWS chloraminated, % | 17.7 | 37.9 | 38.3 | 8.6 | 2.8 | NA |
| Surface water as source for PWS, % | 5.2 | 28.1 | 15.9 | 55.7 | 11.7 | NA |
| Mean TTHMa, μg/L | 7.3 | 35.0 | 17.5 | 14.9 | 7.9 | NA |
| Smoking status, % | ||||||
| Never | 62.6 | 61.9 | 59.9 | 61.5 | 64.1 | 78.5 |
| Former | 21.2 | 22.5 | 23.1 | 22.6 | 21.0 | 12.3 |
| Current | 16.2 | 15.6 | 17.0 | 15.9 | 14.9 | 9.2 |
| Pack-years smoking, %b | ||||||
| 1-19 | 40.6 | 41.5 | 38.2 | 39.0 | 39.6 | 45.0 |
| 20-39 | 33.3 | 33.6 | 35.2 | 34.0 | 35.3 | 34.4 |
| ≥40 | 26.1 | 24.9 | 26.6 | 27.0 | 25.1 | 20.6 |
| Occupation, % | ||||||
| Homemaker | 33.1 | 33.4 | 32.5 | 31.9 | 35.4 | 52.5 |
| Professional | 16.3 | 16.9 | 15.1 | 16.6 | 15.7 | 12.0 |
| Clerical/craft | 48.8 | 48.1 | 50.9 | 50.6 | 46.7 | 25.7 |
| Farmer | 1.5 | 1.2 | 0.9 | 0.6 | 1.8 | 9.4 |
| Other | 0.4 | 10.5 | 0.7 | 0.3 | 0.4 | 0.4 |
| Residence, % | ||||||
| Farm | 3.2 | 3.3 | 2.1 | 2.2 | 4.2 | 71.3 |
| Rural area (non-farm) | 1.8 | 2.2 | 1.5 | 2.8 | 3.2 | 19.3 |
| City/town | 95.0 | 94.5 | 96.4 | 95.1 | 92.6 | 9.4 |
| Body mass index (BMI), % | ||||||
| <25 | 40.8 | 42.5 | 42.8 | 43.3 | 35.9 | 35.7 |
| 25-29.9 | 37.3 | 36.2 | 35.9 | 36.3 | 37.9 | 38.0 |
| ≥30 | 22.0 | 21.3 | 21.4 | 20.4 | 26.2 | 26.3 |
| Education, % | ||||||
| Less than high school | 6.8 | 6.1 | 6.6 | 5.0 | 7.2 | 10.1 |
| High school | 53.3 | 52.0 | 54.0 | 47.4 | 55.4 | 52.2 |
| More than high school | 39.9 | 42.0 | 39.5 | 47.7 | 37.4 | 37.8 |
| Diabetes, % | 5.9 | 5.8 | 5.6 | 5.3 | 5.6 | 4.9 |
| Physical activity level,% | ||||||
| Low | 46.4 | 47.1 | 48.1 | 46.2 | 49.3 | 47.7 |
| Moderate | 28.3 | 27.5 | 26.3 | 26.5 | 25.5 | 28.4 |
| High | 25.4 | 25.4 | 25.6 | 27.3 | 25.2 | 24.0 |
| Oral contraceptive use, ever, % | 20.8 | 20.9 | 19.3 | 18.7 | 20.6 | 18.9 |
| Estrogen use | 40.4 | 39.7 | 40.7 | 43.3 | 34.4 | 34.9 |
| Insulin use, % | ||||||
| No | 98.0 | 97.8 | 98.1 | 97.9 | 97.3 | 98.3 |
| Yes, but not currently | 0.6 | 0.3 | 0.4 | 0.5 | 0.7 | 0.5 |
| Yes, currently | 1.5 | 1.7 | 1.5 | 1.6 | 1.9 | 1.1 |
| Mean age at menopause, years | 47.6 | 47.7 | 47.6 | 47.5 | 48.0 | 48.3 |
| Nitrate in diet, mg/day (median)c | 61.2 | 61.3 | 61.8 | 63.1 | 59.2 | 59.1 |
| Nitrite in diet, mg/day (median)c | 0.64 | 0.64 | 0.65 | 0.65 | 0.65 | 0.66 |
| Nitrite in diet from processed meat, mg/day (median)c | 0.03 | 0.03 | 0.03 | 0.03 | 0.04 | 0.04 |
| Vitamin C in diet, mg/day (median)c | 108.0 | 111.8 | 108.7 | 114.9 | 106.3 | 99.9 |
NA= not applicable
a
Exposures assigned to individuals based on their reported duration at drinking water source. Categories include quartiles 1-3; 75th-95th percentile, and 95th percentile.
b
Among current or former smokers at baseline.
c
Adjusted for 1,000 kcal per day of total energy intake.