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Getting Plant-Based Calcium in the Diet

By Sharon Palmer, MSFS, RDN

Help clients who choose plant-based, dairy-free diets meet calcium needs through plant-based sources.

The plant-based eating trend continues to grow, in particular, in the dairy aisle. An increasing array of plant-based dairy alternatives in supermarkets demonstrates just how popular plant-based, dairy-free diets are among consumers. But how can dietitians ensure their clients get enough calcium? While dairy products do provide calcium in the diet, this important mineral can be found in many plant-based foods. However, it’s important to educate clients on meeting their calcium needs to maintain good health.

Calcium is the most abundant mineral in the body. Most of the body’s calcium is in bones, including teeth, where it plays an integral part in bone structure and contributes to a calcium bank. Bones are gaining and losing this abundant mineral continuously as part of a remodeling process. When calcium intake is adequate, bones benefit; when intake is low, bones suffer. The body takes calcium from bones when it isn’t getting enough calcium in the diet, which can lead to weakened bones. Vitamin D, along with regular exercise, helps the body absorb and process calcium, too.

What’s more, nutrients such as protein, magnesium, and antioxidants play critical roles in maintaining bone health. So, it’s important to ensure clients are getting adequate sources of these nutrients for bone health, too. In addition to bone health, calcium is important for other body functions, such as muscle contractions, releasing hormones, and transmitting messages through the nerves.

Calcium in a Plant-Based Diet
Getting enough calcium in a plant-based diet is possible, but it requires some planning. In a plant-based eating style, calcium can be found in dark leafy vegetables like broccoli and kale, beans, soy products, nuts, seeds, certain grains, and calcium-fortified foods and drinks. If possible, the best way for clients to receive calcium is from food sources. However, low-dose calcium supplements can be a helpful addition for those struggling to meet their needs.

 RDA for Calcium

Age Male Female Pregnant Lactating
0 to 6 months (AI)* 200 mg 200 mg N/A N/A
7 to 12 months (AI)* 260 mg 260 mg N/A N/A
1 to 3 years 700 mg 700 mg N/A N/A
4 to 8 years 1,000 mg 1,000 mg N/A N/A
9 to 13 years 1,300 mg 1,300 mg N/A N/A
14 to 18 years 1,300 mg 1,300 mg 1,300 mg 1,300 mg
19 to 50 years 1,000 mg 1,000 mg 1,000 mg 1,000 mg
51 to 70 years 1,000 mg 1,200 mg N/A N/A
> 70 years 1,200 mg 1,200 mg N/A N/A

Source: Calcium. National Institutes of Health website. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/. Updated October 6, 2022.

*AI = Adequate Intake

Increasing Calcium Absorption
Clients can help the absorption of calcium by increasing vitamin D and C intake. Calcium, vitamin D, and vitamin C play different roles in maintaining bone health. Individuals can get vitamin D from sun exposure, but absorption is dependent on several factors, such as geographical location, skin pigment, and duration in the sun. Most people don’t get enough vitamin D from the sun and need to consume vitamin D in their diet to meet their needs.

Plant-based food sources of vitamin D include mushrooms exposed to light, fortified orange juice, and fortified plant milks. Vitamin C synthesizes collagen and maintains cartilage found in bones and teeth. Vitamin C can be found in many fruits and vegetables, including cruciferous vegetables, peppers, and citrus fruits.

Calcium Bioavailability
Calcium absorption is dependent on calcium bioavailability, which describes how well the body absorbs and uses nutrients. Dairy sources of calcium contain more calcium but still may have a lower bioavailability (about 30%) than some plant sources of calcium, like bok choy, kale, and broccoli (about 50%). Recommending more bioavailable food sources of calcium may enable clients to meet their needs for this mineral, as well as maintain an overall nutritionally balanced diet.

Sources of highly bioavailable calcium (> 50%) include the following:

• kohlrabi, 13.4 mg of 20 mg absorbed (67%);
• cauliflower, 11.7 mg of 17 mg absorbed (68.6%);
• green cabbage, 16.2 mg of 25 mg absorbed (64.9%);
• Brussels sprouts, 12.1 mg of 19 mg absorbed (63.8%);
• broccoli, 21.5 mg of 35 mg absorbed (61.3%);
• bok choy, 42.5 mg of 79 mg absorbed (53.8%);
• watercress, 13.4 mg of 20 mg absorbed (67%); and
• radish, 10.4 mg of 14 mg absorbed (74.4%).

Antinutrients and Calcium
Some plant foods, such as spinach, sweet potatoes, and legumes contain oxalic acid and phytates. Oxalates and phytates, referred to as antinutrients, are naturally occurring plant compounds that can bind to calcium and inhibit their absorption. High-oxalate sources of calcium, like spinach and chard, may not be as available to the body as cruciferous, low-oxalate sources, such as kale, broccoli, and mustard greens.

Avoiding foods with oxalates isn’t necessary, as they still provide nutritional benefits. Instead, be aware of which foods contain oxalates and ensure adequate sources of calcium are included in the diet to make up for decreased absorption. Moreover, individuals can reduce antinutrient compounds during the process of cooking, fermenting, sprouting, or soaking foods, such as nuts, grains, and pulses.

By working with clients individually to help them get adequate sources of calcium in their daily diets, RDs can ensure good health.

Low-Moderate Oxalate Plant-Based Calcium Sources

Food Serving Size Calcium (mg) Calcium (% DV)
Collard greens 1 cup, chopped, cooked 268 mg 27%
Chickpeas 1 cup, cooked 239 mg 24%
Dried figs 1 cup (149 g) 241 mg 24%
Black-eyed peas 1/2 cup cooked 185 mg 19%
Bok choy 1 cup, cooked 158 mg 16%
Seaweed, nori 1 cup, raw 126 mg 13%
Sunflower seeds 1 cup 109 mg 11%
Kale 1 cup, chopped, cooked 94 mg 9%
Broccoli 1 cup, cooked 61 mg 6 %

Sources: Jack Norris, RD, Vegan Health; https://veganhealth.org/calcium/calcium-part-3/; https://ucikidneystonecenter.com/wp-content/uploads/2020/06/Oxalate-Content-of-Foods.pdf

— Sharon Palmer, MSFS, RDN, is The Plant-Powered Dietitian, author of the new book The Plant-Powered Plan to Beat Diabetes, and nutrition editor of Today’s Dietitian.