Table 4.

Effect Modification of the Association Between an Interquartile Range^a Increase in Toenail Arsenic Concentration and QT Duration by Antioxidant Nutrient Intake Among a Subset of Normative Aging Study Participants (n = 198), Boston, Massachusetts, 2000–2002^b

Antioxidant Intake Scorec	Change in QT, ms	95% Confidence Interval	Change in QTc, ms	95% Confidence Interval
Low intake (n = 55)	11*	0.078, 22	4.1	−4.1, 12
Intermediate intake (n = 83)	2.7	−4.2, 9.6	0.24	−6.3, 6.8
High intake (n = 60)	3.2	−1.9, 8.4	3.9	−0.04, 7.9
Pinteraction	0.28		0.95

Abbreviations: ms, millisecond(s); QTc, heart rate-corrected QT.

^*P < 0.05 (2 sided).

^aCorresponding to a 0.059-μg/g increment of toenail arsenic concentration.

^bAll multivariate linear regression models are adjusted for age, cigarette smoking (smoker vs. nonsmoker), pack-years of smoking, season of clinical visit, body mass index, serum C-reactive protein, serum fasting glucose, year of clinical visit, mean arterial pressure, and daily total energy intake.

^cTo assess modification by antioxidant intake, we constructed a score representing the combined intake of vitamin C, vitamin A, and total carotene. For each nutrient, we assigned participants a score of 1–3, corresponding to their tertile of intake. The overall intake score was obtained by summing scores for individual dietary components and was partitioned into 3 categories: low (3–4), intermediate (5–7), or high (8–9).