Drink milk? We’ve all heard that calcium, an essential nutrient for building and maintaining strong bones, is a dietary must-have, especially for women. Thin, Caucasian and Asian women have the highest risk for osteoporosis, where the bones become porous and fracture easily, but all women are at risk — and so are men.

“Most adults need approximately 1,000 milligrams of calcium daily, and one cup of yogurt (400 milligrams) or milk (280-300 milligrams) goes far in helping reach this goal,” says Mindy Haar, Ph.D., a registered dietitian and the director of program development in the Department of Interdisciplinary Health Sciences at New York Institute of Technology. Cheese is another good option, with 270 milligrams in one ounce of Swiss.

But what if you're vegetarian, vegan or lactose-intolerant? Since the body best absorbs calcium that occurs naturally in food, here are some good sources:

  • Dark leafy greens (90 milligrams of calcium in a cup of kale)
  • Almonds (95 milligrams in 1/4 cup)
  • Sunflower seeds (50 milligrams in 1 ounce)

Another option that probably comes to mind are foods fortified with calcium. But are they a good bet? Haar says fortified foods can be an excellent source of calcium, especially for those who don't or can't consume any dairy products. Orange juice, soy milk and rice milk are not naturally rich in calcium, but they are fortified to provide amounts on par with milk (about 260 milligrams per cup), says Haar. But there are some caveats — and disagreements — about the practice.

Do calcium-fortified foods improve bone health?

The fortification of foods with calcium started with orange juice and then spread to other juices and milks like hemp, almond and soy. Today, products including breakfast bars, oatmeal and cereal are fortified with calcium.

“Everyone is trying to make foods better and so much more nutritious than they really are so they add calcium to orange juice, soy milk, almond milk to make them more nutritious, but this type of calcium isn’t the same as calcium that occurs naturally in foods,” says Liz Malgieri, RD, CDN, nutrition director at Woodstock Apothecary, an integrative pharmacy that counsels patients in nutrition.

The calcium present in foods naturally is totally different from the calcium that is supplemented in foods, Malgieri says. Supplemented calcium, called calcium carbonate, is derived from rocks, ground oysters and algae; it’s basically a chalklike substance that raises blood calcium levels but really has no value in bone health, she adds.

Sometimes calcium carbonate is combined with citric acid to make calcium citrate, which is another popular supplement added to foods. Again this type may have poor absorption, and there is little research to show it helps build or maintain bone health, Malgieri says.

The downside of supplements

Because calcium carbonate and calcium citrate are absorbed poorly, they can stick to already formed plaque in the bloodstream and create formations like kidney stones if they build up, Malgieri says. “If you already have atherosclerosis [hardening of arteries], it can lead to things like decreased blood flow that cause heart attack and stroke.”

Malgieri thinks people avoid dairy out of fear of antibiotics and hormones — or in the name of a healthy eating plan like veganism — but the marketing behind these fortified foods makes it seem as if they are as nutritious as cow’s milk, when that may not be true.

The only way to know if your calcium supplementation is working is through a bone density scan, which isn’t recommended for women under the age of 65. Malgieri says the answer lies in educating people that cheap calcium supplements or food supplemented with the nutrient aren’t going to do the same for you as foods that are naturally rich in calcium.

“There is really only one type of calcium supplementation that’s really been proven to help with bone density both with maintenance and growth, and it comes from bones — cow bones or fish bones, they both are used in pill supplements.” These calcium supplements, called microcrystalline hydroxyapatite or MCHA, are the next best option for a high absorption rate after foods naturally high in calcium, she says. “So in that instance, if someone is at risk for osteoporosis or wants to supplement their diet with calcium, I would recommend that,” Malgieri says.

How calcium is absorbed

“Many factors can influence how well calcium is absorbed through the digestive system and made available for the body. An acidic medium, such as one created in the stomach during a meal, as well as the presence of other substances such as lactose can enhance absorption,” Haar says. The presence of oxalates, phytates and tannins — which occur naturally in fruits, vegetables and grains — can have a negative effect.

When synthetic or naturally occurring calcium is added to food, it’s hard to say exactly how much is absorbed by the body, Haar says. Not enough studies have been conducted, and some of the studies that have been done were not conducted on humans, she says. Plus, some of the studies were funded by manufacturers of certain types of calcium fortifiers.

“I feel the bottom line is that for those who can eat dairy products, to consume at least three servings a day as well as broccoli, cooked greens and sesame seeds,” Haar says. “Calcium is used in the preparation of tofu, which adds to its content. And I still feel that calcium-fortified orange juice and soy milk can be beneficial.”

Why you should eat calcium-rich foods
There's a big difference between calcium-rich foods and food fortified with calcium, but what's better? Registered dietitian Mindy Haar breaks it down.