. Author manuscript; available in PMC: 2009 Sep 3.

Published in final edited form as: Am J Epidemiol. 2007 Dec 20;167(5):553–560. doi: 10.1093/aje/kwm338

TABLE 4.

Joint effects of black tea intake on cigarette smoking and caffeine intake in relation to Parkinson's disease risk, The Singapore Chinese Health Study, 1993-2005

	Black tea intake
	Nondrinker/occasional			Weekly/daily
	No. of cases	RR^*,^†	95% CI^*	No. of cases	RR^†	95% CI
Smoking status
Never smoker	97	1.00		20	0.57	0.35, 0.93
Ever smoker	31	0.48	0.31, 0.75	9	0.33	0.16, 0.68
Caffeine intake
Below median	80	1.00		19	0.84	0.50, 1.39
Above median	48	0.76	0.53, 1.09	10	0.30	0.16, 0.59

RR, relative risk; CI, confidence interval

^†

All RRs were adjusted for age at recruitment (years), year of interview (1993-1995, 1996-1998), gender, dialect (Hokkien, Cantonese), and level of education (no formal education, primary school, secondary school or higher); for smoking status, RRs were further adjusted for caffeine intake (mg/day); for caffeine intake, RRs were further adjusted for smoking status (never, former, or current smoker).