Impact of l-citrulline supplementation and whole-body vibration training on arterial stiffness and leg muscle function in obese postmenopausal women with high blood pressure
Introduction
Increased aortic stiffness may contribute to the higher prevalence of systolic hypertension (Berry et al., 2004) and heart failure in older women (Coutinho et al., 2013). Carotid–femoral pulse wave velocity (PWV) is considered the gold standard measure of arterial stiffness (O'Rourke et al., 2002). Alternatively, brachial-ankle PWV (baPWV), which mainly includes carotid–femoral PWV (cfPWV) and femoral-ankle PWV (faPWV), has been proposed as an index of central arterial stiffness (Sugawara et al., 2005). Thus, both cfPWV and baPWV are similarly associated with age and systolic blood pressure (BP) (Choo et al., 2014, Tanaka et al., 2009) and are predictors of cardiovascular events and mortality (Vlachopoulos et al., 2010, Vlachopoulos et al., 2012). Although faPWV is less affected by aging, accumulating evidence suggests that leg arterial stiffness (femoral and faPWV) is clinically relevant as positively associates with systolic BP (SBP) (Choo et al., 2014, Park et al., 2010), central adiposity (Park et al., 2010, Snijder et al., 2004), and cardiovascular events and mortality (van Sloten et al., 2014).
Increased PWV may be involved in the age-related loss of muscle mass known as sarcopenia, which preferentially affects the legs in women (Abbatecola et al., 2012, Kohara et al., 2012, Ochi et al., 2010, Snijder et al., 2004). Several studies have shown that sarcopenia is inversely associated with cfPWV (Abbatecola et al., 2012) and baPWV (Kohara et al., 2012, Ochi et al., 2010, Sanada et al., 2010). This relationship appears to be more important for women than men (Sanada et al., 2010). Moreover, the increased mortality risk in postmenopausal women with sarcopenia (Batsis et al., 2014) may be related to the increased cardiovascular mortality associated with high PWV (van Sloten et al., 2014, Vlachopoulos et al., 2010, Vlachopoulos et al., 2012). Since high leg lean mass (LM) is the strongest determinant of reduced aortic and leg arterial stiffness in older adults (Snijder et al., 2004), improvements in leg LM may result in cardiovascular benefits in postmenopausal women.
High-intensity resistance training (RT) is an effective exercise mode for improving mass muscle and strength in postmenopausal women (Casey et al., 2007, Figueroa et al., 2003). However, RT may increase cfPWV and faPWV in middle-aged adults with high SBP (Collier et al., 2008). Alternatively, there is increased evidence to support that whole-body vibration exercise training (WBVT), which is generally performed as a type of RT, is as effective as RT for improving muscle strength and mass in postmenopausal women (Machado et al., 2010, Verschueren et al., 2004). Although it has been shown that WBVT can decrease baPWV and faPWV in older adults (Figueroa et al., 2014b, Lai et al., 2014), a reduction in cfPWV has not been observed. A recent meta-analysis suggested that RT is not an effective intervention for reducing PWV (Ashor et al., 2014). Thus, addition of a nutritional intervention to exercise training may be essential to positively affect PWV.
l-Citrulline, a non-protein amino acid naturally found in watermelon, is efficiently converted to l-arginine, the substrate for endothelial production of nitric oxide (NO), a potent vasodilator (Schwedhelm et al., 2008). l-Citrulline, either synthetic or from watermelon extract, has shown to reduce baPWV and faPWV in middle-aged adults (Figueroa et al., 2013b, Ochiai et al., 2012). Interestingly, improved leg muscle blood flow has been proposed as a mechanism for the increased muscle mass in older adults (Dillon et al., 2011). Therefore, it is possible that the addition of l-citrulline to WBVT may reduce PWV and increase leg LM in postmenopausal women.
The purpose of this study was to investigate the independent and additive effects of l-citrulline supplementation and WBVT on PWV and muscle function in obese postmenopausal women. It was hypothesized that WBVT with l-citrulline supplementation would have greater improvements in PWV and leg muscle strength/mass than either intervention alone. Moreover, WBVT and l-citrulline alone would reduce PWV; however, l-citrulline supplementation would not alter muscle strength.
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Participants
Forty-one women volunteered for a randomized, parallel-design study to evaluate the independent and combined effects of l-citrulline supplementation and WBVT on PWV, BP, and muscle function. Participants were postmenopausal (≥ 1 year without menstruation), overweight or obese (BMI ≥ 30 kg/m2) with prehypertension or stage-1 hypertension, nonsmokers, and sedentary (< 60 min of aerobic exercise/week and no RT during the past 6 months). Medical-history questionnaires were used to screen for chronic
Participants
The WBVT and WBVT + l-citrulline completed at least 99.7 ± 1.1% of the exercise session. Compliance to the supplementation was 95.8 ± 3.0%, 97.5 ± 2.7%, and 96.4 ± 3.6% for the WBVT, l-citrulline, and WBVT + l-citrulline groups. Participant characteristics are shown in Table 1. There were no significant differences in characteristics (Table 1) and arterial parameters (Table 2) at baseline.
Arterial parameters
PWV of the 3 arterial segments are shown in Table 2. There was a significant group-by-time interaction for cfPWV (P <
Discussion
The main findings of our study were that l-citrulline supplementation added to WBVT reduced cfPWV and increased leg LM index in obese postmenopausal women with prehypertension or stage-1 hypertension. Moreover, the three interventions decreased systemic and leg arterial stiffness as measured by baPWV and faPWV.
Increased cfPWV leads to systolic hypertension, preferentially in older women (Berry et al., 2004), and to higher risk for cardiovascular events and mortality (Vlachopoulos et al., 2010).
Conclusion
In conclusion, 8 weeks of combined WBVT and l-citrulline supplementation improved aortic stiffness and muscle function in obese postmenopausal women. Although 8 weeks of l-citrulline and WBVT alone reduced leg arterial stiffness, l-citrulline had no effect on muscle function while WBVT increased muscle strength but not LM index. Therefore, WBVT + l-citrulline supplementation could be an alternative intervention for counteracting the effects of aging and obesity on arterial stiffness and leg
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
The authors wish to thank Performance Health Systems and NOW Foods for providing the whole-body vibration machines and l-citrulline capsules, respectively.
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