Table 2. Multivariable-adjusted HRs (95% CIs) of metabolic syndrome by quartiles (Q) of toenail chromium levels, the CARDIA study, 1987 to 2010 (n = 3,648)^*.

	Quartile of toenail chromium levels				P for linear trend†
	Q1 (lowest)	Q2	Q3	Q4(highest)
Chromium- ppm	<0.266	0.266–0.551	0.552–1.225	≥1.226
No. of participants	912	913	912	912
No. of events	242	246	210	180
Incidence rate-/1000 person years	15.01	14.95	12.63	10.59
Model 1‡	1 (Referent)	1.02 (0.86–1.23)	0.89 (0.74–1.07)	0.76 (0.63–0.93)	0.002
Model 2§	1 (Referent)	0.97 (0.81–1.16)	0.87 (0.72–1.05)	0.74 (0.61–0.90)	0.003
Model 3||	1 (Referent)	0.97 (0.80–1.16)	0.88 (0.72–1.06)	0.80 (0.66–0.98)	0.006

Abbreviations: CARDIA, Coronary Artery Risk Development in Young Adults; CI, Confidence interval; HR, Hazard ratio; LCn-3PUFA, long chain n-3 polyunsaturated fatty acids; Q, quartile.

^*All models were constructed using Cox proportional hazards regression analysis.

^†P for trend was examined by using the continuous variable of toenail chromium levels.

^‡Model 1: adjusted for age (years, continuous), sex, ethnicity (African American or Caucasian), and study center.

^§Model 2: model 1 with additional adjustment for BMI(<18.5, 18.5–24.9, 25–30, ≥30 kg/m²), education(<12, ≥12, years), family history of diabetes(yes or no), smoking status(never smokers, former smokers, or current smokers), alcohol consumption(0,0.1–9.9,10.0–19.9, ≥20g/day), physical activity(quartiles), and intakes (quartiles) of LCn-3PUFA and magnesium.

^||Model 3: model 2(except baseline body mass index, because it is highly correlated with waist circumference) with additional adjustment for individual components of metabolic syndrome at baseline.