Purpose: To evaluate the distribution of lipoprotein(a) (Lp(a)) and assess its association to cardiovascular disease (CVD) in American Indians.
Methods: Lp(a) was measured in 3991 American Indians (aged 45-74 years with no prior history of CVD at baseline) from 13 communities in Arizona, Oklahoma, and South/North Dakota. They were followed prospectively from 1989 to 1997 for CVD. The distribution of Lp(a) was examined by center, sex, and diabetic status. Spearman correlation coefficients and Cox regression models were used to evaluate the association of Lp(a) to CVD.
Results: A total of 388 participants subsequently developed CVD. Median Lp(a) concentration in American Indians was 3.0 mg/dl. This was almost half of that in whites and one sixth in blacks from the CARDIA study measured by the same method. Nondiabetic participants had significantly higher Lp(a) levels than diabetic participants for both genders. Lp(a) levels were higher in women than in men for nondiabetic participants, but there was no gender difference for diabetic participants. Correlation analysis showed Lp(a) was significantly negatively correlated with the degree of Indian heritage, insulin, triglycerides (TG), fasting plasma glucose (FPG), and 2-hour plasma glucose (2hPG), and positively with low-density lipoproteins (LDL), apoprotein B (apoB), and fibrinogen (FIB). In Cox regression models, adjusting for other risk factors, Lp(a) was no longer a significant predictor of CVD in either diabetic or nondiabetic participants.
Conclusions: The lower concentration of Lp(a) in American Indians and the high correlation with Indian heritage confirm the concept that Lp(a) concentration is in large part genetically determined. Lp(a) concentration is not an independent predictor of CVD among American Indians; it is higher in those who develop CVD because of its positive correlation with LDL, apoB, and FIB.