What are some current issues and controversies about magnesium?
- Magnesium and blood pressure
Evidence suggests that magnesium may play an important role in regulating blood pressure. Diets that provide plenty of fruits and vegetables, which are good sources of potassium and magnesium, are consistently associated with lower blood pressure. The DASH study (Dietary Approaches to Stop Hypertension) suggested that high blood pressure could be significantly lowered by a diet high in magnesium, potassium, and calcium, and low in sodium and fat. In another study, the effect of various nutritional factors on incidence of high blood pressure was examined in over 30,000 U.S. male health professionals. After four years of follow-up, it was found that a greater magnesium intake was significantly associated with a lower risk of hypertension. The evidence is strong enough that the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure recommends maintaining an adequate magnesium intake as a positive lifestyle modification for preventing and managing high blood pressure.
- Magnesium and heart disease
Magnesium deficiency can cause metabolic changes that may contribute to heart attacks and strokes. There is also evidence that low body stores of magnesium increase the risk of abnormal heart rhythms, which may increase the risk of complications associated with a heart attack. Population surveys have associated higher blood levels of magnesium with lower risk of coronary heart disease. In addition, dietary surveys have suggested that a higher magnesium intake is associated with a lower risk of stroke. Further studies are needed to understand the complex relationships between dietary magnesium intake, indicators of magnesium status, and heart disease.
- Magnesium and osteoporosis
Magnesium deficiency may be a risk factor for postmenopausal osteoporosis. This may be due to the fact that magnesium deficiency alters calcium metabolism and the hormone that regulates calcium. Several studies have suggested that magnesium supplementation may improve bone mineral density, but researchers believe that further investigation on the role of magnesium in bone metabolism and osteoporosis is needed.
- Magnesium and diabetes
Magnesium is important to carbohydrate metabolism. It may influence the release and activity of insulin, the hormone that helps control blood glucose levels. Elevated blood glucose levels increase the loss of magnesium in the urine, which in turn lowers blood levels of magnesium. This explains why low blood levels of magnesium (hypomagnesemia) are seen in poorly controlled type 1 and type 2 diabetes.
In 1992, the American Diabetes Association issued a consensus statement that concluded: "Adequate dietary magnesium intake can generally be achieved by a nutritionally balanced meal plan as recommended by the American Diabetes Association." It recommended that "... only diabetic patients at high risk of hypomagnesemia should have total serum (blood) magnesium assessed, and such levels should be repleted (replaced) only if hypomagnesemia can be demonstrated.”
What is the health risk of too much magnesium?Dietary magnesium does not pose a health risk, however very high doses of magnesium supplements, which may be added to laxatives, can promote adverse effects such as diarrhea. Magnesium toxicity is more often associated with kidney failure, when the kidney loses the ability to remove excess magnesium. Very large doses of laxatives also have been associated with magnesium toxicity, even with normal kidney function. The elderly are at risk of magnesium toxicity because kidney function declines with age and they are more likely to take magnesium-containing laxatives and antacids.
Signs of excess magnesium can be similar to magnesium deficiency and include mental status changes, nausea, diarrhea, appetite loss, muscle weakness, difficulty breathing, extremely low blood pressure, and irregular heartbeat.
The Institute of Medicine of the National Academy of Sciences has established a tolerable upper intake level (UL) for supplementary magnesium for adolescents and adults at 350 mg daily. As intake increases above the UL, the risk of adverse effects increases.
This Fact Sheet was developed by the Clinical Nutrition Service, Warren Grant Magnuson Clinical Center, National Institutes of Health (NIH), Bethesda, MD, in conjunction with the Office of Dietary Supplements (ODS) in the Office of the Director of NIH.