Background
Increased left ventricular (LV) mass, or left ventricular hypertrophy (LVH) is an independent risk factor for cardiovascular disease events, and the prevalence of LVH varies between race/ethnic groups [
1]. In a recent analysis of Hispanic, African-American, Chinese, and White participants in the Multi-Ethnic Study of Atherosclerosis (MESA), all Hispanic subgroups had a higher mean LV mass and a higher prevalence of LVH compared with White and Chinese participants at the time of the baseline study examination. Hypertension is strongly associated with the presence of LVH, but the race/ethnic differences in LV mass observed in MESA were not easily explained by a higher prevalence of hypertension among all of the Hispanic subgroups. In fact, Mexican-American participants had a higher mean LV mass and a higher prevalence of LVH compared with White and Chinese participants despite having a similar prevalence of hypertension and similar mean blood pressures [
2].
Acculturation is the adoption of the traditions, values, attitudes and cultural practices of another country [
3]. Acculturation may involve stress-related processes as well as behavioral changes. A number of studies have linked higher acculturation to a higher prevalence of hypertension [
4‐
7]. Consistent with most, but not all prior studies, an analysis from MESA found that acculturation was associated with hypertension [
5]. However, the association between acculturation parameters and hypertension within race/ethnic groups in this sample was not reported due to lack of statistical power. Given the strong association between hypertension and LVH, a positive association between greater acculturation and LVH would be expected. Acculturation may in part explain the relatively higher LV mass among Hispanic participants, when compared to other race/ethnic groups.
We used data from MESA to examine the associations between acculturation and LV mass. We hypothesized that a higher degree of acculturation, calculated using an acculturation score and acculturation characteristics: i) place of birth in or outside of the U.S.; ii) English vs. non-English language spoken at home; and iii) number of years living in the U.S. (in immigrants), would be associated with a higher mean LV mass, beyond risks accounted for by traditional risk factors for both acculturation and increased LV mass.
Discussion
This study examined the association between acculturation and LVMI in a multi-ethnic cohort of individuals aged 45–84 years at baseline and who had no discernable clinical cardiovascular disease. From the findings, higher levels of acculturation are associated with increased LVMI. Also, LVMI varied by language spoken at home and time spent in the U.S. but not by nativity; different measures of acculturation appeared to have varying effects in differences race/ethnic groups, highlighting the complexity of the acculturation concept.
Among foreign-born participants, having lived in the U.S. for longer periods of time was associated with a higher mean LVMI, even after adjusting for traditional CVD risk factors. In fact mean LVMI increased after 20 or more years of residence in the U.S., compared to those who had lived in the U.S. for less than 20 years. Evidence suggests that the health advantage exhibited by foreign-born individuals over U.S.-born individuals tends to decrease with duration of stay in the U.S. [
18,
19]. This decline in the health with increased duration of stay in the U.S. has also been reported for other health measures like obesity [
16,
19‐
21] and heart disease [
22]. One explanation could be that some immigrant groups (non-U.S. Whites, Hispanics, and Asians) may be less likely, than U.S.-born individuals, to discuss dietary or physical activity measures with their clinicians, [
19] probably in part due to patient-provider characteristics which affect care such as language barriers and cultural sensitivity.
Participants who spoke exclusively English at home had higher LVMI compared to those who spoke a language other than English. This finding may be explained by the fact that those who spoke exclusively English may have been either those born in the U.S. or those who had lived in the U.S. for longer periods of time. Ninety-seven percent of Blacks (91 % born in the U.S.) and 97 % of non-Hispanic Whites (94 % born in the U.S.) spoke exclusively English at home. These may have been participants with higher acculturation levels (96 % of non-Hispanic whites and 92 % of Blacks had an acculturation score of 5). This finding corroborates with an analysis using the same cohort which showed a higher prevalence of hypertension, a strong predictor of LVMI, among those who spoke English at home [
5]. Other studies have described different associations between language spoken and hypertension. In one study, those who spoke Russian at home reported a higher prevalence of hypertension than those who spoke English [
23]. This was attributed to a higher baseline prevalence of self-reported hypertension among those born in Eastern/Central Europe, than US-born whites.
In our study, the association between acculturation and LVMI did not differ when birthplace alone was considered (U.S.-born vs. foreign-born). This finding may be attributed to the fact that among participants born out of the U.S. (33 % of sample), the majority (76 %) had lived in the U.S. for at least 10 years and thus may have had acculturation levels comparable to those born in the U.S.
The race/ethnic stratified analysis demonstrates the complexity and heterogeneity of the associations of acculturation measures and LVMI among the different immigrant groups. Overall, blacks had higher mean LVMI than other race/ethnic groups. This risk was even higher among foreign-born than U.S.-born blacks. The increased risk in blacks may be due to a number of factors including psychosocial stress, chronic adrenergic stimulation [
24,
25] and increased sodium retention, [
26] both of which are disproportionately increased in blacks. An association between these factors and increased LVMI has been described in other studies [
27,
28]. Place of birth, and not language spoken at home, may have been an important dimension of acculturation among blacks in the US (who may be from Haiti, the Caribbean, or Africa) since many countries in the Caribbean and in Africa already have English as the national language. Among Hispanics, preferential English speaking at home (greater acculturation) was associated with increased LVMI. There is strong evidence that points towards a negative effect of greater acculturation and health behaviors, including diet, illicit drug, alcohol and tobacco use, [
29] all of which are associated with increased LVMI [
30‐
32].
Despite having higher levels of physical activity, the most acculturated participants had higher mean LVMI. Similarly, blacks with the highest total number of hours of exercise per week had the highest mean LVMI of all ethnicities; Chinese with the least total number of hours of exercise had the least mean LVMI. The fact that the more acculturated participants were more physically active despite having higher LVMI may be explained by a number of factors. First, physical activity may not be an important factor contributing to decreased LVMI in our sample. This is consistent with results from one study which showed that fat mass, rather than inactivity, is an important contributor to disease risk in young Mexican and Mexican–American women [
33]. Second, our measure of physical activity (hours of exercise per week) may not be a good correlate of the effects of exercise on LVMI.
To the best of our knowledge, this is the first study investigating the association between acculturation and LVMI. The multiethnic nature of our sample makes it possible to compare the independent associations of measures of acculturation among the different race/ethnic groups. However, the cross-sectional nature of our analysis makes it impossible to draw any inferences on a causal link between acculturation and LVMI. Another limitation of our study is the scope of our measure of acculturation which may have influenced some of our non-significant findings. Several studies have used different surrogates for acculturation, and our measure may not fully cover the spectrum of acculturation and its related cardiovascular health effects. It is therefore important to consider the measures of acculturation used and outcomes under study when comparing our findings with that of other studies. Also, due to sample size limitations of our race/ethnic stratified analyses, we may have had insufficient power to detect the presence of other associations between measures of acculturation and LVMI among race/ethnic groups. Finally, residual confounding via measurement error may possibly explain some of the associations found, although we would expect significant associations given the results of other studies examining acculturation and other health effects. Our study nevertheless found significant associations between acculturation measures and increased LVMI.
Regardless of the process of acculturation, lifestyle modification (via physical activity, diet, and smoking cessation) provides cardiovascular health benefits. The present study, however, identifies a group a group of individuals (more acculturated) which is at risk of developing increased LVM, and consequently CVD. This reinforces the notion that the immigrant process and making decisions on retaining one’s native culture while adapting to a new culture may exert a remarkable stress on cardiovascular health behaviors and subsequent health risks in certain individuals due to factors such as lack of healthcare access and social marginalization which will impede healthy lifestyle modifications.
Acknowledgements
The authors thank the other investigators, the staff, and the participants of the MESA study for their valuable contributions. A full list of participating MESA investigators and institutions can be found at
http://www.mesa-nhlbi.org.
This research was supported by contracts N01-HC-95159, N01-HC-95160, N01-HC-95161, N01-HC-95162, N01-HC-95163, N01-HC-95164, N01-HC-95165, N01-HC-95166, N01-HC-95167, N01-HC-95168 and N01-HC-95169 from the National Heart, Lung, and Blood Institute and by grants UL1-TR-000040 and UL1-TR-001079 from NCRR. The research was also partially supported by NHLBI grant R01 HL104199 (Epidemiologic Determinants of Cardiac Structure and Function among Hispanics).
Competing interests
The authors have no competing interests.
Authors’ contributions
VSE contributed to the study methodology, literature review, interpretation and discussion of findings, and manuscript write-up; HC contributed to study conception, data analysis and interpretation of findings; AM, AGB, and DAB contributed to study conception, study design, and performed a critical review; TS contributed to data interpretation and performed a critical review of manuscript; CD and KEW contributed to data interpretation and performed a critical review of manuscript; CJR contributed to study conception and design, data acquisition, interpretation of findings, and manuscript write-up. All authors read and approved the final manuscript for publication.