How much calcium do I really need?

DEAR DOCTOR K:

I’m a 65-year-old woman. My doctor says my bones are strong, and he wants to keep them that way. So, for years I’ve been taking a daily 1,200 milligram calcium supplement. Now I hear that might be too much. How much calcium do I really need?

DEAR READER:

I’ve gotten this question from so many patients. As I assume is true for you, their bones have normal amounts of calcium. That is, they do not have osteoporosis (or “thin bones”). To prevent osteoporosis, they have been taking the recommended amount of calcium — 1,000 milligrams (mg) a day for women ages 50 and younger and 1,200 mg for women over 50 — in an effort to preserve their bones.

It is true that the majority of studies show that a combination of calcium and vitamin D supplements reduce the risk of developing osteoporosis. So far, so good.

But the main reason to prevent osteoporosis is to reduce the risk of bone fractures. And most studies find that calcium supplements (or even calcium plus vitamin D) do not reduce that risk. Worse, calcium supplements may even increase other health risks.

One study involved postmenopausal women enrolled in the Women’s Health Initiative trial. Some 18,000 women were randomly assigned to take 1,000 mg of calcium and 400 international units (IU) of vitamin D each day. (Vitamin D works with calcium to build healthy bones.) Another 18,000 women got placebo pills. After seven years, women who took calcium and vitamin D were no less likely to break their hips than the women who took a placebo pill.

Another study analyzed the results of more than a dozen studies. It found that women (and men) who had a high calcium intake — from food or pills — did not have a lower hip fracture risk.

The studies also revealed that high-dose calcium supplements can lead to an increased risk of kidney stones and heart attack. Calcium from food did not have the same risks.

What to do? My colleague Dr. Walter Willett, chair of the Department of Nutrition at Harvard T.H. Chan School of Public Health, recommends less calcium and more vitamin D than the guidelines suggest. He suggests 500 to 700 mg a day of calcium and 800 to 1,000 IU of vitamin D. Current guidelines recommend 600 IU of vitamin D between ages 19 and 70 years, and 800 IU after age 70. While not everyone agrees with him, I regard Dr. Willett as one of the world’s most knowledgeable experts in this area. I’ve seen him proven right a lot more often than wrong.

At Dr. Willett’s suggested amount, you can probably get all or most of your calcium from food. Dairy products are a great source. Kale, collard greens and salmon are good non-dairy calcium sources. (I’ve put a table listing more calcium-containing foods at the end of this post.)

You can take a low-dose calcium supplement to make up what you don’t get from food. Keeping your calcium supplement dose lower should help you avoid the possible risks of higher-dose supplements.

25 sources of dietary calcium

Produce Serving size Estimated calcium in milligrams
Collard greens, frozen 8 oz 360
Broccoli rabe 8 oz 200
Kale, frozen 8 oz 180
Soy Beans, green, boiled 8 oz 175
Bok Choy, cooked, boiled 8 oz 160
Figs, dried 2 figs 65
Broccoli, fresh, cooked 8 oz 60
Oranges 1 whole 55
Seafood Serving size Estimated calcium
Sardines, canned with bones 3 oz 325
Salmon, canned with bones 3 oz 180
Shrimp, canned 3 oz 125
Dairy Serving size Estimated calcium
Ricotta, part-skim 4 oz 335
Yogurt, plain, low-fat 6 oz 310
Milk, skim, low-fat, whole 8 oz 300
Yogurt with fruit, low-fat 6 oz 260
Mozzarella, part-skim 1 oz 210
Cheddar 1 oz 205
Greek yogurt 6 oz 200
American cheese 1 oz 195
Feta cheese 4 oz 140
Cottage cheese 4 oz 125
Fortified food Serving Size Estimated calcium
Almond milk, rice milk or soy milk, fortified 8 oz 300
Tofu, prepared with calcium 4 oz 205
Orange juice fortified with calcium 4 oz 150
Cereal, fortified 8 oz 100-1,000
Source: International Osteoporosis Foundation