Abstract 090: Does Dietary Sodium Contribute to the Discordance in Blood Pressures among Monozygotic Twins?

Abstract

Background: Dietary sodium (Na) and central adiposity are considered important risk factors for hypertension (HTN). Blood pressure (BP) levels are discordant among 40-50% of monozygotic (MZ) twin pairs. One prior study of MZ twins using questionnaires reported that hypertensive (HT) MZ twins differed in their intake of meat and milk. However, none of the previous studies have evaluated the impact of Na intake on BP in MZ twins. Methods: Eighty-eight pairs of MZ twins were enrolled from Milwaukee, WI and Michigan State University Twin Registry, East Lansing, MI (age- 44 ± 9 years, 63% women, and 96% Caucasian). BPs (measured in triplicate and averaged) and anthropometrics were measured. Na intake was calculated using Block Sodium Screener. Twin pairs were considered concordant or discordant based on systolic (SBP) or diastolic BP (DBP) difference of 10 mm Hg between co-twins, off BP medications Results: Thirty-seven twin pairs were discordant in their BP levels. Mean (± SD, mm Hg) SBP/DBPs among concordant and discordant twins were 120 ± 12 / 77 ± 9 and 131 ± 18 / 81 ± 10 respectively. Mean differences in SBP/DBP among concordant and discordant twins were 5 ± 7 / 4 ± 4 and 14 ± 8 / 10 ± 6 respectively. Discordant twins as a group had higher waist circumference (WC) compared to concordant twins (p<0.05), but with no differences in BMI or Na intake. However, among the discordant twin pairs, the co-twin with higher BPs (138 ± 18 / 85 ± 9) had higher dietary salt intakes (3900 ± 1437 vs. 3261 ± 1058 mg/d) and higher WC (105 ± 15 vs. 98 ± 18 cm) (p=0.02) compared to their co-twin with lower BPs (121 ± 16 / 77 ± 9). The average Na intake among the concordant twins was 3443 ± 1189 mg/day. Differences in Na intake among discordant co-twins remained statistically significant after adjustment for age, gender, BMI, WC, and waist-to-hip ratio. Conclusions: Higher Na intake is associated with higher BPs among MZ twins with discordant BPs. Differences in Na intakes were significant independent of central adiposity indicating significant Na sensitivity in discordant MZ twin pairs. The effect of ~500mg less Na intake/day in resulting in lower BPs in genetically identical individuals, suggests that modest decreases in Na-intake in Na-sensitive individuals may be sufficient to see the desired effect on BP levels.