Table 1. Baseline characteristic of studies included in the systematic review and meta-analysis.
| Variable | IMRCC [35] | NLCS [36] | EPIC [37] | ATBC [38] | NHS [39] | HPFS [39] | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cases | Non-cases | Cases | Non-cases | Cases | Non-cases | Cases | Non-cases | Cases | Non-cases | Cases | Non-cases | |
| Country | Italy | Netherlands | 10 countries in Europe | Finland | USA | USA | ||||||
| Study design | Case control | Case cohort | Case control | Nested case control | Cohort | Cohort | ||||||
| Assessment of exposure | FFQ | FFQ | Plasma samples | Plasma samples | FFQ | FFQ | ||||||
| Study quality | 7 | 8 | 9 | 8 | 8 | 8 | ||||||
| Sample size | 767 | 1534 | 314 | 4438 | 556 | 556 | 224 | 224 | 225 | 76983 | 211 | 47675 |
| Mean age (years) | 62.0 | 62.0 | 61.9 | 61.4 | 56.9 | 56.9 | 57.0 | 57.0 | 61.0 | 61.0 | 62.0 | 62.0 |
| Sex (percentage male) | 64.4 | 64.4 | 65.9 | 49.4 | 56.0 | 56.0 | 100 | 100 | 0 | 0 | 100 | 100 |
| Education (< 7 years) | 48.5 | 55.3 | - | - | 41.0 | 37.0 | 79.5 | 78.6 | - | - | - | - |
| Education (7–11 years) | 27.6 | 29.8 | - | - | 22.0 | 25.0 | - | - | - | - | - | - |
| Education (> 11 years) | 23.9 | 14.9 | - | - | 37.0 | 39.0 | - | - | - | - | - | - |
| BMI (< 25) | 36.8 | 36.7 | Mean: 25.5 | Mean: 25.0 | 32.0 | 40.0 | Mean: 26.7 | Mean: 25.9 | - | - | - | - |
| BMI (25–30) | 45.4 | 49.1 | 45.0 | 43.0 | - | - | - | - | ||||
| BMI (> 30) | 17.8 | 14.2 | 23.0 | 16.0 | - | - | - | - | ||||
| Smoking (never) | 41.1 | 41.7 | 24.8 | 35.8 | 41.0 | 44.0 | - | - | - | - | - | - |
| Smoking (current) | 30.8 | 30.4 | 36.3 | 28.3 | 30.0 | 23.0 | - | - | - | - | - | - |
| Smoking (ex-smokers) | 28.1 | 27.9 | 38.9 | 35.9 | 29.0 | 32.0 | - | - | - | - | - | - |
| Alcohol (never) | 17.1 | 15.1 | - | - | 7.0 | 4.0 | Mean: 7.4 | Mean: 11.2 | Mean: 6.0 | Mean: 6.0 | Mean: 11.0 | Mean: 11.0 |
| Alcohol (current) | 74.7 | 77.5 | - | - | 92.0 | 95.0 | ||||||
| Alcohol (ex-drinkers) | 8.2 | 7.4 | - | - | 2.0 | 1.0 | ||||||
| History of hypertension (yes) | 35.0 | 25.0 | - | - | 37.0 | 37.0 | 32.0 | 32.0 | ||||
| History of hypertension (no) | 50.0 | 59.0 | - | - | 63.0 | 63.0 | 68.0 | 68.0 | ||||
| Adjusted factors | Period of interview, education, BMI, smoking, alcohol intake and family history of kidney cancer | Age, sex, smoking, BMI and history of hypertension | Waist-to-hip ratio, hypertension, educational attainment, smoking status, plasma cotinine, alcohol intake at recruitment and alcohol intake. | Age, BMI and smoking; folate additionally adjusted for protein and fat; vitamin B6, riboflavin and homocysteine additionally adjusted for serum folate; vitamin B12 additionally adjusted for protein, leisure-time physical activity and serum folate. | Age, smoking status, BMI, history of hypertension, history of diabetes, physical activity, fruit and vegetable intake, alcohol intake, and parity | Age, smoking status, BMI, history of hypertension, history of diabetes, physical activity, fruit and vegetable intake, and alcohol intake | ||||||