A potential role for zinc in restless legs syndrome

Correlates of Restless Legs Syndrome in Older People

Background: We examined the association between restless legs syndrome (RLS) and comprehensive geriatric assessment (CGA) data in two older European populations. The second goal was to evaluate correlates of their quality of life (QoL). Methods: Diagnostic criteria of the International RLS Study Group (IRLSSG) and elements of CGA were used in this study. Results: Among the examined 246 participants, 77 (31.3%) suffered from RLS, more often in the UK (39.4%) than in Poland (25.4%) (p = 0.019). In the multivariate logistic regression model, female sex [OR (CI) = 3.29 (1.51-7.21); p = 0.0014], the number of medications per day [OR (CI) = 1.11 (1.02-1.20); p = 0.011] and alcohol consumption [OR (CI) = 5.41 (2.67-10.95); p < 0.001] increased the probability of RLS. Residing in Poland [OR (CI) = 3.06 (1.36-6.88); p = 0.005], the presence of RLS [OR (CI) = 2.90 (1.36-6.17); p = 0.004], chronic heart failure, [OR (CI) = 3.60 (1.75-7.41); p < 0.001], osteoarthritis [OR (CI) = 2.85 (1.47-5.49); p = 0.0016], and urinary incontinence [OR (CI) = 4.74 (1.87-11.9); p < 0.001] were associated with a higher probability of mobility dimension problems in the QoL. Higher physical activity was related to a lower probability of mobility problems [OR (CI) = 0.85 (0.78-0.92); p < 0.001]. Conclusions: female sex, the number of medications and alcohol consumption are independent correlates of RLS in older adults. RLS together with several chronic medical conditions and a low physical activity level were independent correlates of the mobility dimension of the QoL.

Review of the role of the endogenous opioid and melanocortin systems in the restless legs syndrome

Restless legs syndrome (RLS) is responsive to opioid, dopaminergic and iron-based treatments. Receptor blocker studies in RLS patients suggest that the therapeutic efficacy of opioids is specific to the opioid receptor and mediated indirectly through the dopaminergic system. An RLS autopsy study reveals decreases in endogenous opioids, β-endorphin and perhaps Met-enkephalin in the thalamus of RLS patients. A total opioid receptor knock-out (mu, delta and kappa) and a mu-opioid receptor knock-out mouse model of RLS show circadian motor changes akin to RLS and, although both models show sensory changes, the mu-opioid receptor knock mouse shows circadian sensory changes closest to those seen in idiopathic RLS. Both models show changes in striatal dopamine, anaemia and low serum iron. However, only in the total receptor knock-out mouse do we see the decreases in serum ferritin that are normally found in RLS. There are also decreases in serum iron when wild-type mice are administered a mu-opioid receptor blocker. In addition, the mu-opioid receptor knock-out mouse also shows increases in striatal zinc paralleling similar changes in RLS. Adrenocorticotropic hormone and α-melanocyte stimulating hormone are derived from pro-opiomelanocortin as is β-endorphin. However, they cause RLS-like symptoms and periodic limb movements when injected intraventricularly into rats. These results collectively suggest that an endogenous opioid deficiency is pathogenetic to RLS and that an altered melanocortin system may be causal to RLS as well.

Associations of serum zinc, copper, and selenium with sleep disorders in the American adults: Data from NHANES 2011-2016

BACKGROUND

Even though various studies have been conducted to investigate the relationship between trace metals and sleep, few epidemiological studies have evaluated the relationship between trace metals and sleep disorders in American adults.

OBJECTIVE

This study intended to evaluate the associations of serum zinc (Zn), copper (Cu), selenium (Se), Zn/Cu, Zn/Se, and Cu/Se ratios with sleep disorders in American adults.

METHODS

We conducted a cross-sectional analysis of 3660 adults aged ≥18 years old who participated in the National Health and Nutrition Examination Survey (NHANES) 2011-2016. Binary logistic regression was employed to calculate the odds ratio (OR) and 95 % confidence interval (CI) of either serum trace metals or serum trace metals ratios with risks among sleep disorder phenotypes. The restricted cubic spline (RCS) model was additionally utilized to check the dose-response relationships between serum trace metals, serum trace metals ratios, and sleep disorders.

RESULTS

Logistic regression demonstrated that higher serum Zn (OR: 0.70, 95 % CI: 0.51-0.97, p = 0.035), Zn/Cu (OR: 0.62, 95 % CI: 0.45-0.87, p = 0.007), and Zn/Se (OR: 0.68, 95 % CI: 0.49-0.95, p = 0.025) were related to a decreased likelihood of self-reported sleep disorders, and dose-response relationships were detected by the RCS models, after adjustment for sociodemographic, behavioral, and health characteristics. No associations between serum Cu, Se, Cu/Se, and sleep disorders were observed. The findings in the sensitivity analyses were consistent with these results.

CONCLUSION

Our study revealed that serum Zn, Zn/Cu, and Zn/Se were inversely associated with the risk of self-reported sleep disorders in US adults.

Prevalence and Determinants of Restless Legs Syndrome (Willis-Ekbom Disease) in an Older Greek Population

OBJECTIVES

The present study aimed to explore the descriptive and analytic epidemiology of restless legs syndrome (RLS) in the older Greek population, with a specific focus on lifestyle indicators.

METHODS

Baseline data from the randomly selected non-demented older participants of the population-based HELIAD cohort were analyzed. Multivariable binary logistic regression with RLS diagnosis as the dichotomous dependent outcome was performed. Demographic, socioeconomic, anthropometric, dietary, sleep-related and psychological parameters, physical activity, use of psychoactive substances and personal medical history were investigated for potential associations.

RESULTS

A total of 133 from the eligible sample of 1,838 participants were diagnosed with RLS. The mean age-sex standardized prevalence of RLS among the elderly was estimated at 6.1% (95%CI = 5.0-7.2), with a female (8.0%, 95%CI = 6.4-9.6) to male (3.7%, 95%CI = 2.4-5.1) ratio of 2.1. The prevalence of RLS peaked during the 8^th decade of life and diminished thereafter. The positive associations of RLS with female sex [OR = 2.06, 95%CI = (1.19-3.57)], anxiety levels [assessed by the 22-point HADS scale, OR = 1.08, 95%CI = (1.03-1.13)] and traumatic brain injury [OR = 2.22, 95%CI = (1.37-3.62)] were reproduced. Good sleep quality was related to 55% [95%CI~(24-83%)] lower odds of having RLS in comparison with both poor and moderate quality. Adherence to the Mediterranean dietary pattern [assessed by a 55-point scale, OR = 1.06, 95%CI = (1.01-1.11)], and low daily energy intake [low-moderate vs. low: OR = 0.45, 95%CI = (0.26-0.79)]; [moderate-high vs. low: OR = 0.69, 95%CI = (0.40-1.22)]; [high vs. low: OR = 0.31, 95%CI = (0.13-0.69)] were related to RLS for the first time.

CONCLUSIONS

More emphasis should be placed on the dietary-nutritional aspects of RLS.

Serum Trace Elements Concentrations in Patients with Restless Legs Syndrome

Increased brain and serum zinc levels in patients with idiopathic restless legs syndrome (idiopathic RLS or iRLS) were described when compared with controls, suggesting a possible role of zinc in the pathogenesis of this disease. However, serum magnesium, calcium, manganese, iron, and copper levels of RLS patients were similar to controls, suggesting a specific impairment of zinc-dependent metabolism in RLS. The aim of this study is to assess the serum concentrations of trace elements involved in oxidative stress or causing peripheral nerve toxicity in a large series of patients with iRLS and controls. We determined serum levels of iron, copper, manganese, zinc, magnesium, selenium, calcium, aluminium, lead, cadmium, arsenic and mercury in 100 patients diagnosed with iRLS and in 110 age- and sex-matched controls using Inductively Coupled Plasma Mass Spectrometry. Serum copper, magnesium, selenium, and calcium concentrations were significantly higher in RLS patients than in controls. These differences were observed both in men and women. There were no major correlations between serum trace metal concentrations and age at onset of RLS or RLS severity, nor was there any association with a family history of RLS or drug response. This study shows an association between increased serum concentrations of copper, magnesium, selenium, and calcium with RLS in a Spanish Caucasian population and does not confirm the previously reported increase in serum zinc concentrations in patients suffering from this disease, suggesting that the different accuracy of the analytical methods used could have influenced the inconsistent results found in the literature.