Browsing by Author "He, Ka"

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    The Circulating Concentration and 24-h Urine Excretion of Magnesium Dose- and Time-Dependently Respond to Oral Magnesium Supplementation in a Meta-Analysis of Randomized Controlled Trials
    (Oxford, 2016-03) Zhang, Xi; Del Gobbo, Liana C.; Hruby, Adela; Rosanoff, Andrea; He, Ka; Dai, Qi; Costello, Rebecca B.; Zhang, Wen; Song, Yiqing; Epidemiology, School of Public Health
    Background: Accurate determination of Mg status is important for improving nutritional assessment and clinical risk stratification. Objective: We aimed to quantify the overall responsiveness of Mg biomarkers to oral Mg supplementation among adults without severe diseases and their dose- and time responses using available data from randomized controlled trials (RCTs). Methods: We identified 48 Mg supplementation trials (n = 2131) through searches of MEDLINE and the Cochrane Library up to November 2014. Random-effects meta-analysis was used to estimate weighted mean differences of biomarker concentrations between intervention and placebo groups. Restricted cubic splines were used to determine the dose- and time responses of Mg biomarkers to supplementation. Results: Among the 35 biomarkers assessed, serum, plasma, and urine Mg were most commonly measured. Elemental Mg supplementation doses ranged from 197 to 994 mg/d. Trials ranged from 3 wk to 5 y (median: 12 wk). Mg supplementation significantly elevated circulating Mg by 0.04 mmol/L (95% CI: 0.02, 0.06) and 24-h urine Mg excretion by 1.52 mmol/24 h (95% CI: 1.20, 1.83) as compared to placebo. Circulating Mg concentrations and 24-h urine Mg excretion responded to Mg supplementation in a dose- and time-dependent manner, gradually reaching a steady state at doses of 300 mg/d and 400 mg/d, or after ~20 wk and 40 wk, respectively (all P-nonlinearity ≤ 0.001). The higher the circulating Mg concentration at baseline, the lower the responsiveness of circulating Mg to supplementation, and the higher the urinary excretion (all P-linearity < 0.05). In addition, RBC Mg, fecal Mg, and urine calcium were significantly more elevated by Mg supplementation than by placebo (all P-values < 0.05), but there is insufficient evidence to determine their responses to increasing Mg doses. Conclusions: This meta-analysis of RCTs demonstrated significant dose- and time responses of circulating Mg concentration and 24-h urine Mg excretion to oral Mg supplementation.
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    Serum magnesium concentration and incident cognitive impairment: the reasons for geographic and racial differences in stroke study
    (Springer, 2021) Chen, Cheng; Xun, Pengcheng; Unverzagt, Frederick; McClure, Leslie A.; Ryan Irvin, Marguerite; Judd, Suzanne; Cushman, Mary; He, Ka; Psychiatry, School of Medicine
    Purpose: To examine the prospective association between serum Mg level and the incidence of cognitive impairment. Methods: A random sub-cohort (n = 2063) from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) cohort was included in this study. Baseline serum Mg concentration was measured using inductively coupled plasma mass spectrometry. According to the current reference interval of serum magnesium (0.75-0.95 mmol/L), we classified participants below the interval as Level 1 and used it as the referent. The rest of the study population were equally divided into three groups, named Level 2 to 4. Incident cognitive impairment was identified using the Six-Item Screener. Multivariable-adjusted odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were estimated using logistic regression models. Results: After adjustment for potential confounders, an inverse threshold association between serum Mg level and incident cognitive impairment was observed. Compared to those with hypomagnesemia (Level 1: < 0.75 mmol/L), the relative odds of incident cognitive impairment was reduced by 41% in the second level [OR (95% CI) = 0.59 (0.37, 0.94)]; higher serum Mg level did not provide further benefits [Level 3 and 4 versus Level 1: OR (95% CI) = 0.54 (0.34, 0.88) and 0.59 (0.36, 0.96), P for linear trend = 0.08]. Conclusions: Findings from this prospective study suggest that sufficient Mg status within the normal range may be beneficial to cognitive health in the US general population.
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    Serum mercury concentration and the risk of ischemic stroke: The REasons for Geographic and Racial Differences in Stroke Trace Element Study
    (Elsevier, 2018-08) Chen, Cheng; Xun, Pengcheng; McClure, Leslie A.; Brockman, John; MacDonald, Leslie; Cushman, Mary; Cai, Jianwen; Kamendulis, Lisa; Mackey, Jason; He, Ka; Neurology, School of Medicine
    BACKGROUND: Although biologically plausible, epidemiological evidence linking exposure to methylmercury with increased risk of ischemic stroke is limited. The effects of methylmercury may be modified by selenium, which is an anti-oxidant that often co-exists with mercury in fish. OBJECTIVES: To examine the association between serum mercury levels with the incidence of ischemic stroke and to explore the possible effect modifications by serum selenium levels and demographic and geographic factors. METHODS: A case-cohort study was designed nested in the REasons for Geographic and Racial Differences in Stroke cohort, including 662 adjudicated incident cases of ischemic stroke and 2494 participants in a randomly selected sub-cohort. Serum mercury was measured using samples collected at recruitment. Multivariable-adjusted hazard ratios (HRs) and the corresponding 95% confidence intervals (CIs) were estimated using the Barlow-weighting method for the Cox proportional hazards regression model. RESULTS: No statistically significant association was observed between serum mercury concentration and the incidence of ischemic stroke (the highest vs. lowest quintile of mercury levels: HR = 0.82; 95% CI = 0.55-1.22; P for linear trend = 0.42). Sex (P for interaction = 0.06), but not serum selenium levels, modified the association; a more evident trend toward lower incidence of ischemic stroke with higher mercury levels was observed among women. CONCLUSION: This study does not support an association between mercury and the incidence of ischemic stroke within a population with low-to-moderate level of exposure. Further studies are needed to explore the possibility of mercury-induced ischemic stroke toxicity in other populations at higher exposure levels.