When Popeye declared, "I'm strong to the finish, 'cause I eats me spinach!" he probably had no idea why spinach had such powers.

It turns out that in addition to providing around 30% of your daily value for vitamin C, 12% of B6, 8% of iron, and 6% of calcium in just 3.5 ounces, it's also dishing up 6% of the magnesium your body needs. That helps muscles, nerves, bones, and heart function smoothly, and protects you from vitamin D deficiency.

And now it turns out it's also important for brain health.

A study published in the European Journal of Nutrition found that getting more than 550 mg of magnesium a day is associated with greater brain volume and a younger brain age, especially in women. (The recommended daily allowance for adults age 19 to 51 is 400 mg-420 mg daily for men and 310 mg-320 mg for women.)

Other studies indicate that getting magnesium from food provides more benefits getting it than from supplements — maybe because of its interaction with certain other nutrients.

To get it, enjoy spinach, Swiss chard, almonds, cashews, peanuts, beans, salmon, poultry, bananas, and 70% dark chocolate.

People with Type 2 diabetes are at particular risk for magnesium deficiency because insulin resistance increases urination, which flushes out magnesium. And some medications, including diuretics and proton pump inhibitors for acid reflux, deplete magnesium.

To check your level, get a total serum magnesium blood test (a healthy level is 2.1 mg/dL or a bit higher). There are also tests of magnesium levels in urine and red blood cells.