The highest intake of magnesium was associated with a 28 per cent reduction in the risk of gallstones, according to the study with 42,705 male Americans published in The American Journal of Gastroenterology .
"In this large cohort study, we observed that a higher consumption of magnesium was associated with a reduced risk of gallstone disease with a dose-response relationship that was not accounted for by other potential risk factors including other measured dietary variables," wrote lead author Chung-Jyi Tsai from the University of Kentucky Medical Center.
Gallstone disease is a major source of morbidity in developed countries and an important risk factor for gallbladder cancer.
About 10-15 per cent of the US population (20 million people) have gallstones, and 1 million new cases are diagnosed yearly, according to the US National Institutes of Health.
Tsai, in collaboration with researchers from Brigham and Women's Hospital and Harvard Medical School, Harvard School of Public Health, and the National Cancer Institute, assessed the consumption of magnesium among the study population (average age 52.6, average BMI 24.8 kg per sq. m) using a validated semi-quantitative 131-item food frequency questionnaire (FFQ).
Over the course of an average of 13 years of follow-up, the researchers documented 2,195 cases of gallstones.
The average intake of magnesium was calculated to 352.8 milligrams per day for the study population.
After adjusting the results to account for age differences, which may affect the results, Tsai and co-workers calculated that men with the highest levels of magnesium intake (454 mg/d) were 28 per cent less likely to develop gallstones, compared to men with the lowest average intake (262 mg/d).
Moreover, dietary magnesium, which include sources like green, leafy vegetables, meats, starches, grains and nuts, and milk, were found to decrease the risk by 32 oer cent.
"The exact mechanism of magnesium intake in preventing gallstone disease is not clear and can be multi factorial," wrote the authors.
"Hyperinsulinemia and insulin resistance are known to be positively associated with gallstone disease."
"Low magnesium consumption has been associated with high fasting insulin concentrations.
Chronic hypersecretion of insulin, a feature of insulin resistance, may increase the cholesterol saturation index in the bile, and thus may facilitate gallstone formation," they added.
"In animal and clinical studies, a magnesium-deficient diet can elevate plasma triglycerides and decrease plasma HDL-cholesterol levels, and thus may increase the risk for gallstones."
The authors did not conduct a mechanistic study, but previous studies clearly suggest potential modes of protection for the mineral.
"In conclusion, our findings suggest a protective role of magnesium consumption in the prevention of symptomatic gallstone disease among men," wrote Tsia and co-workers.
Asking the right questions In an accompanying editorial, Cynthia Ko from the University of Washington in Seattle made important points concerning the study results.
"The primary outcome of this study was symptomatic gallstone disease and cholecystectomy - the most advanced stages of gallstone-related diseases.
These results suggest that low magnesium intake predisposes to symptomatic gallstones.
However, these results cannot necessarily be generalized to asymptomatic gallstones, which comprise the majority of all gallstones," she said.
"Therefore, we cannot determine where in the pathophysiological process leading to symptomatic gallstones is magnesium intake important.
"For example, does higher magnesium intake protect against initial formation of gallbladder sludge and stones?
Or, does higher magnesium intake decrease the likelihood of the already existing gallstones becoming symptomatic?
Or both?" asked Ko.
Earlier dietary surveys show that a large portion of adults does not meet the RDA for magnesium (320 mg per day for women and 420 mg per day for men).
Source: The American Journal of Gastroenterology (Blackwell Publishing) February 2008, Volume 103, Issue 2, Pages 375-382, doi:10.1111/j.1572-0241.2007.01696.x "Long-Term Effect of Magnesium Consumption on the Risk of Symptomatic Gallstone Disease Among Men" Authors: C.-J. Tsai, M.F. Leitzmann, W.C. Willett, E.L. Giovannucci Editorial: The American Journal of Gastroenterology February 2008, Volume 103, Issue 2, Pages 383-385, doi:10.1111/j.1572-0241.2007.01690.x "Magnesium: Does a Mineral Prevent Gallstones?"
Author: C.W. Ko