Descriptive Characteristics by racial ancestry
At baseline (1987-1989), the total sample consisted of 10,681 participants (8,451 (79.1%) White and 2,230 (20.0%) African American) aged 45-64 years. Included in the total sample, MetS cases at baseline and during 11-years of follow-up included 43.0% and 50.5% among Whites and 49.2% and 55.8% among African Americans, respectively.
Table 1 shows the baseline characteristics of participants included in the analyses. All characteristics were significantly different between Whites and African Americans except total cholesterol and LDL cholesterol. A higher proportion of African Americans smoked cigarettes, had a high-school education or less, were on blood pressure medications or were obese; additionally, they had lower levels of physical activity, higher systolic and diastolic blood pressure, higher fasting blood glucose, and higher triglyceride levels compared to Whites. In contrast, a higher proportion of Whites were current drinkers and the mean HDL cholesterol was lower, but fewer had diabetes or MetS compared to African Americans.
Association between GRS or dietary patterns and MetS
The GRS was associated with MetS in both Whites and African Americans (Table 2). Each 5-increment increase in the GRS posed higher risk for MetS among African Americans (p <.001). Additionally, the highest GRS tertile had the greatest risk for MetS compared to the lowest tertile among Whites (RR=1.28; CI:1.23-1.33, p <.001) and notably in African Americans (RR=1.37; CI:1.27-1.48; p <.001).
In longitudinal analyses, the Western dietary pattern increased MetS risk among Whites (RR=1.21; CI:1.12-1.31; p < .001). In contrast, the high-fat dairy pattern was associated with lower risk for MetS among Whites (RR)=0.72; CI:0.66-0.79; p <.001) and African Americans (RR=0.81; CI:0.69-0.96; p=.013); see Table 2.
Interaction between the GRS and Dietary Patterns on MetS
We observed interactions with the GRS and dietary patterns (Table 3). The greatest protective effects were observed for the high-fat dairy pattern in the lowest GRS tertile among Whites (RR=0.62; CI:0.52-0.74; p <.001) and African Americans (RR=0.67; CI:0.49-0.91; p <.011). However, African Americans with the greatest burden of high-risk alleles (highest GRS tertile) and those who consumed a healthy diet, had a higher risk for MetS (RR=1.39; CI:1.07-1.82; p=.015). Among African Americans, the overall effect of the GRS and the Western dietary pattern increased MetS risk (RR=7.43; CI:1.57-35.08; p=.011). However, the confidence intervals were very wide for the point estimate and appeared unstable.
Association between dietary patterns and resolution or development of MetS
Because MetS is comprised of individual risk factors that can improve or worsen over time, participants may have resolution or development MetS during the 11 years of follow-up. We investigated the association of dietary patterns and whether participants became free of MetS at visit 4 or developed MetS at visit 4 after having MetS at visit 1 or were free of MetS at visit 1. In these analyses, participants’ MetS status change was in one direction only from visits 1 to 4. Figure 2 and Supplemental Table 4 show the associations of dietary patterns with resolution or development of MetS at visit 4 by racial ancestry. Compared to those who did not have MetS at all four visits, the Western dietary pattern increased MetS risk among Whites: RR=1.64; CI:1.44-1.86; p <.001; n=4,499 for those with MetS at all four visits; RR=1.42; CI:1.19-1.69; p <.001, for those who were free of MetS at visit 1 and risk of developing MetS at visit 4 (n=4,110); and RR=1.60; CI:1.28-2.00; p=.001; n=3,696 for those who had MetS at visit 1 and risk of being free from MetS at visit 4.
In contrast, high-fat diary pattern consistently showed a protective association among Whites.
Compared to those who did not have MetS at all four visits, the relative risks were decreased in the following amounts: RR=0.59; CI:0.50-0.69; p <.001 and risk of MetS at all four visits (n=4,999); RR=0.73; CI:0.61-0.88; p=.001; for those who were free of MetS at visit 1 and risk of developing MetS at visit 4 (4,110); RR=0.72; CI:0.57-0.91; p=.006; and for those who had MetS at visit 1 and risk of being free from MetS at visit 4 (n=3,696).
Among African Americans, the healthy dietary pattern was associated with higher risk for MetS (RR=1.65; CI:1.15-2.16; p= <.001; n=1,010) for those who had MetS at all four visits. The high-fat dairy patterns showed significant protective risks: RR=0.66; CI:0.45-0.98; p=.038; n=1,026 among those who had MetS at visit 1 and risk of being free from MetS at visit 4. However, the latter estimates did not meet the Bonferroni threshold or multiple testing (p <.017).
Interaction between the GRS and Dietary Patterns and resolution or development of MetS
We investigated whether the GRS and dietary patterns interact to influence MetS risk beyond their independent associations. As in association analyses above, participants’ MetS status change was in one direction only from visits 1 to 4. We present results only for dietary patterns that showed significant associations with the GRS in Figure 3. Supplemental Tables 5A and 5B show all significant and non-significant associations for dietary patterns and GRS tertiles by racial ancestry. We scaled dietary patterns as per 5-increment within the GRS tertiles. As in the association analysis, in all these analyses, the comparator was those who did not have MetS at any of the four visits. Among Whites who had MetS at all four visits (n=4,499), we observed higher risks for the Western dietary pattern within the GRS tertiles (p values for GRS tertiles 1, 2 and 3: .003, .001, .001, respectively). Conversely, in spite of the risk-raising GRS, the protective effects of high-fat dairy in the interaction remain among Whites for decreased risk of MetS at all four visits (p values for GRS tertiles 1, 2 and 3: .001, .003, .001, respectively; overall interaction effect: RR=0.08; CI:0.01-0.47; p=.005). However, the greatest protection for the high-fat dairy pattern was in the lowest GRS tertile for Whites (RR=0.47; CI:0.33-0.66; p ≤ .001; n=1,637) and African Americans (only significant in the lowest tertile; RR=0.67; CI:0.50-0.91; p ≤ .009; n=1,661) who were free of MetS at visit 1 and risk of developing MetS at visit 4.
Among African Americans who had MetS at visit 1 but were free of MetS at visit 4 compared to participants without MetS at all 4-visits, there was a protective effect of high-fat dairy intake in the second tertile (RR=0.33; CI:0.15-0.68); p=.003; n=367; overall interaction effect: RR=0.0076; CI:0.0002-0.3372; p=.012; n=1,026). The lowest GRS tertile (RR=0.45; CI:0.21-0.94; p=.033; n=358) was statistically significant but did not met Bonferroni correction for multiple testing (P <.017). Moreover, in the highest GRS tertile for those who had MetS at all four visits, the healthy dietary pattern was associated with increased MetS risk (RR=2.08; CI:1.48-2.92; p <.001; n=310). In addition, there was a harmful effect of the healthy dietary pattern for those who had MetS at visit 1 and risk of being free from MetS at visit 4 (RR=3.61; CI:1.66-7.87; p <.001; n=240).
Association between dietary patterns for those who had resolution or development of MetS whose MetS status cycled between visits 1 and 4
We investigated the association of dietary patterns in participants whose MetS status cycle between visits 1 through 4. Supplemental Table 6 shows the associations for dietary patterns and associations with MetS among MetS status cyclers by racial ancestry. In these analyses, participants reverted back-and-forth from being free of MetS to having MetS or vice-versa from visits 1 to 4. Participants were free from or had MetS at visit 1. Among Whites, the Western dietary pattern was associated with higher risk for MetS at visit 4 (RR=1.66; CI:1.30-2.12; p <.001; n=3,477); as well as less likely to remain free from MetS at visit 4 (RR=1.43; CI:1.13-1.81; p=.003; n=3,706). However, the magnitude of effect was higher for Whites for the former association. High-fat dairy intake was associated with decreased risk of MetS in Whites (RR=0.76; CI:0.60-0.96; p=.019; n=3,706) and African Americans (RR=0.66; CI:0.45-0.96; p=.028; n=986) and the likelihood of being free from MetS at visit 4, but this association did not meet the Bonferroni threshold cutoff of p <.017.
Interaction between a GRS and dietary patterns for those who had resolution or development of MetS whose MetS status cycled between visits 1 and 4
We investigated the interaction between the GRS and dietary patterns in participants whose MetS status cycle between visits 1 through 4. Supplemental Table 7A and 7B show the interactions of a GRS and dietary pattern associations with MetS among MetS status cyclers by racial ancestry. As stated above, in these analyses, participants reverted back-and-forth from being free of MetS to having MetS or vice-versa. In these analyses we combined participants who were free from or had MetS at visit 1 to augment our sample. We observed higher risks for MetS at visit 4 among Whites in the lowest (RR=1.77; CI:1.19-2.74; p=.005; n=1,394) and highest (RR=1.72; CI:1.18-2.52; p=.005; n=1.020) GRS tertiles for the Western pattern. Similarly, there was a less likelihood for being free from MetS at visit 4 in the highest GRS tertile for the Western dietary pattern (RR=1.68; CI:1.14-2.47; p=.008; n=1,094). In contrast, the high-fat dairy pattern was protective of MetS in the lowest GRS tertile and showed a decreased risk of MetS at visit 4 (RR=0.51; CI:0.32-0.81; p <.004; n=1,394); and for those who remained free of MetS at visit 4 (RR=0.64; CI:0.44-0.95; p=.027; n=1,490), but the latter association did not meet the Bonferroni threshold for multiple testing (p <.017).
Among African Americans whose MetS status cycled between visits 1 to 4, we observed the harmful effects of the Western dietary pattern was significant only in the highest GRS tertiles for those who had MetS at visit 4 (RR=0.32; CI:0.16-0.67; p=.002; n=227). The high-fat dairy pattern was protective in the second GRS tertile and showed a favorable risk of being free from MetS at visit 4 (RR=0.46; CI:0.24-0.89; p=0.20; n=354), but the association did not meet the Bonferroni threshold for multiple testing (p <.017).
Molecular genetic clustering pathway analysis
We used Literature Lab™ clustering analysis to find functional relationship differences among the genes by racial ancestry. Fewer genes but more metabolic pathways were found in African Americans than Whites (Figures 4 and 5). In general, the top pathways for African Americans included pathways that were identified in Whites, as well as additional pathways for obesity and related body fat distribution, and lipid and carbohydrate metabolism. This may indicate that mechanisms involving gene-diet and disease risks may be more complex among African Americans than Whites.
The top five pathways by association for Whites were linoleic acid with FAD1 (26.0%) and FAD2 (67.5%), regulation of insulin secretion with insulin (88.7%), type 2 diabetes with insulin (78.5%), pancreatic secretion with insulin (70.9%), and fatty acid elongation with FAD1 (38.8%) and FAD2 (60.1%). When we categorized pathways by the most significant p values, the top pathways for Whites were CHREBP and MLXIPL (99.2%), vitamin D receptor and vitamin D (99.8%), and GCPRs-Class A Rhodopsin-Like and Rhodopsin (100%). For African Americans the top pathways by association were, CHREBP and MLXIPL (99.6%), G-Alpha signaling (99.9%) and BDNF (99.9%) with GNAS. The top five strongest pathways by most significant p values for African Americans were linoleic acid metabolism with FAD2 (66.7%) and FAD1 (26.8%) genes, followed by insulin secretion and type 2 diabetes with insulin pathway (86.1% and 83.1%), respectively, in addition to vitamin A and carotenoid metabolism with CY26A1 (55%) and ALDH1A2 (38.6%), and maturity onset diabetes with insulin (82.2%).
We examined similarities by association among pathways for Whites compared with African Americans and found vitamin A and carotenoid metabolism with ALDH1A2 (94.7% vs. 38.6%), ketone body regulation with insulin (89% vs. 90%), fructose/mannose metabolism with MXIPL (86.2% vs. 86.3%), glucose and energy metabolism with insulin (84.3% vs. 83.7%), and unsaturated fatty acid biosynthesis with FAD2 (55.8% vs. 55.8%) and FAD1 (44.2% vs. 44.1%) were the top pathways with a nutrition focus. We examined similarities by p value among Whites compared with African Americans, and found additional genes for CHREBP and MXIPL (99.2% vs 99.6%) and linoleic acid metabolism with FAD1 (67.5% vs. 69.7%) and FAD2 (26% vs. 26.8%).
We compared differences in the pathways among racial ancestry by score, and observed that apoptosis and insulin cellular apoptosis were the top pathways. The genes associated with these pathways were: BCL2 for Whites (92.3% and 88.4%) and African Americans RELA (38% and 30%), and PPAR for Whites (20.2% and 20.9%). We looked at differences among pathways by p value for Whites/African Americans, and found CHREBP with MXIPL (99.2% /99.6%) and linoleic acid metabolism with FAD1 (67.5% vs. 69.7%) and FAD2 (26% vs. 26.8%) were statistically significant at p <.0001.