This essential nutrient isn’t the most popular supplement on store shelves—but maybe it should be

Vitamin E is an antioxidant and a component of all cell membranes, so when it’s in short supply, all cells can suffer. Yet it’s estimated that at least 90 percent of Americans don’t get a minimum of 15 mg daily—the amount considered adequate for most people—from food alone.

Severe deficiency is rare and usually stems from a genetic defect that impairs normal absorption and metabolism of vitamin E. Symptoms can include loss of muscle control, nerve damage, muscle weakness, and damage to the retina of the eye. More common, subtle deficiencies can contribute to faster skin aging, joint degeneration, heart disease, loss of memory, and other mental faculties in later years, vision deterioration, and higher risk for some cancers.

Some studies have shown clear benefits of vitamin E supplements while others have not. But as more is learned, some reasons for these conflicting results are emerging.

Individual Differences in Metabolism

A German study published in Nature Communications has discovered that vitamin E may produce benefits in an indirect way. After a person takes vitamin E, the liver produces alpha-carboxychromanol, a metabolite that has anti-inflammatory and other beneficial effects. But the amount produced varies significantly from one person to another.

“If the effect of vitamin E depends on how much of the bioactive metabolite is produced, this explains very well why the same amount of vitamin E has a particular effect in one person and perhaps a much more limited effect in another,” says lead researcher Oliver Werz, PhD.

Forms of Vitamin E

Vitamin E in nature exists in eight forms: alpha-, beta-, gamma-, and delta-tocopherol, and alpha-, beta-, gamma-, and delta-tocotrienol. But major studies have focused on only one: alpha-tocopherol, the only form that is found in human blood where its levels can be measured. Other forms are found in tissues where there’s no way to measure levels.

When studies have looked at other forms of vitamin E, researchers found that they can reduce risk for diabetes, heart disease, and cancer, and may help to relieve digestive, skin, and joint problems.

In supplements and fortified foods, alpha-tocopherol can come in two forms: d-alpha tocopherol, a natural form; and dl-alpha-tocopherol, a synthetic form. When ingested, the natural form is more readily absorbed, so you need smaller amounts. Today, established supplement brands usually contain natural vitamin E.