How much magnesium do you need per day?

A widely used guideline for adults of around 70 kg is a daily intake of roughly 250 mg of magnesium. That figure is based on an estimate of the average requirement of approximately 175 mg per day, with a margin to cover most people. Government supplements to this are sometimes set higher, but a review suggests that the current official standards may be due for revision and could better be calculated per kilogram of body weight.

Can you get those 250 mg from food? With the right choices, yes: spinach, nuts, avocado, whole grains and legumes are the richest sources. In practice, far from everyone reaches that amount. A Japanese study in 62 people found an average intake of around 322 mg per day, but the link between intake and blood levels turned out to be weak. There is a reason for this: blood levels do not give a reliable picture of the total supply in the body. You can have a normal blood level and still have a deficiency in muscles and bones.

Those at extra risk are older adults, especially people in care facilities. Surveys show that intake in older adults regularly falls below the recommended amount. What you eat alongside magnesium also matters: a high calcium intake, low protein and certain fibres can inhibit absorption. Fermentable fibres, on the other hand, appear to promote absorption.

If your diet falls short, supplements are an option, with a safe upper limit of 600 mg per day from supplements as an addition to food. Lower blood levels have been linked in multiple studies to type 2 diabetes, high blood pressure, cardiovascular disease, migraine and Alzheimer's disease, but that is an association, not a proven cause. The average Western diet appears to be sufficient to avoid serious deficiencies, but probably not enough to reach the optimal level.