“You are what you eat,” the saying goes. Or maybe it should be more accurately said, “You are what you absorb.” In a perfect world, you would get all the nutrients necessary for good health from your diet.

Because that’s often not the case, you take supplements as needed. However, many factors can potentially affect the absorption and the bioavailability of the food you eat and the supplements you take: vitamins that work in concert with each other, foods that hinder or help absorption, certain lifestyle choices, age, weight, overall health, and heredity—they all make a difference.

The chart below, though not all-inclusive, will provide you with tips on how to get more from your supplements. Refer to your health practitioner for individualized specifics.

Best supplement combos

Supplement

What helps your body use it

What hinders its effectiveness

Calcium

Adequate levels of vitamins D and C, adequate protein and fat intake, moderate exercise, and milk lactose all assist in calcium absorption. Recent studies indicate that vitamin D supplements can increase calcium absorption by as much as 65 percent. Magnesium—also required for the absorption and utilization of calcium—should be one-half the amount of calcium. Calcium supplements are often chelated with amino acids, such as glutamic or aspartic acid, to make them more absorbable. The amino acid lysine is also necessary for calcium absorption. Food sources of lysine include eggs, fish, beans, and soy products. Citric acid enhances absorption, which is why calcium supplements are sold as calcium citrate and why calcium is added to orange juice.

Stress, lack of exercise, and gastrointestinal problems hinder absorption. A diet rich in foods that contain oxalic acid, such as rhubarb, cocoa or chocolate, chard, and spinach, can interfere with absorption by forming insoluble salts in the gut.

Iron

Adequate levels of vitamin C, copper, cobalt, and manganese help aid iron absorption. The proportions of iron absorbed vary from 2 percent to more than 20 percent, depending partly on other foods eaten at the time of iron intake. Iron absorbed from fortified foods can be increased when eaten with foods high in vitamin C.

Low levels of stomach acid, antacids, and foods high in oxalic acid hinder absorption. Dairy products can interfere with iron absorption if taken at the same time—wait two hours between dairy and iron doses.

Vitamin C

Functions best in concert with vitamins A and E and bioflavonoids. Eat whole foods (for example, an orange rather than orange juice) with vitamin C supplements for enhanced absorption.

Smoking, birth control pills, caffeine, and aspirin can decrease vitamin C levels in the body. Caffeine functions as a diuretic and promotes fluid loss, depleting the body of vitamin C and other water-soluble vitamins.

Vitamin E

A 2004 study found a significant increase in vitamin E absorption rates when taken as food fortified with vitamin E, such as fortified breakfast cereals. The absorption rate decreased when the supplement was taken alone.

Vitamin E absorption is hindered when taken with liquids only or on an empty stomach. Rancid oils, fried foods, and supplemental estrogen deplete vitamin E.