Age and sex adjusted relative risk (with 95% confidence interval (CI)) of developing rheumatoid factor positive rheumatoid arthritis in people taking ⩾4 cups of coffee a day, compared with those taking ⩽3 cups a day, in strata of different factors
| Factor | Stratum | Number of subjects examined | Number of incident cases | Relative risk | 95% CI | p Value for interaction5-150 | |
| Age | <50 years | 11 956 | 58 | 2.14 | 0.96 to 4.77 | ||
| ⩾50 years | 7 025 | 31 | 2.30 | 0.70 to 7.61 | 0.24 | ||
| Sex5-151 | Men | 9 705 | 31 | 3.40 | 1.03 to 11.24 | ||
| Women | 9 276 | 58 | 1.99 | 0.90 to 4.38 | 0.93 | ||
| Serum cholesterol | <7.0 mmol/l | 11 363 | 52 | 1.98 | 0.93 to 4.22 | ||
| ⩾7.0 mmol/l | 7 618 | 37 | 3.97 | 0.95 to 16.50 | 0.78 | ||
| Smoking | Never smoked | 10 067 | 46 | 3.07 | 1.10 to 8.59 | ||
| Quit | 3 411 | 16 | 1.44 | 0.41 to 5.07 | 0.94 | ||
| Current smokers | 5 503 | 27 | 1.90 | 0.57 to 6.39 | |||
| Use of sugar in coffee | No | 5 650 | 21 | 9.16 | 1.22 to 68.63 | ||
| Yes | 13 331 | 68 | 1.56 | 0.77 to 3.15 | 0.23 | ||