The Importance of Milk and Milk Products as Reliable Sources of Calcium
Not only are milk and milk products high in calcium, but the calcium they provide also has good bioavailability, i.e., it is easily accessible to the body. In contrast, most plant sources contain lower amounts and/or less bioavailable calcium.
In Canada, nutrient recommendations (Dietary Reference Intakes [DRIs]) are established in collaboration with the U.S. by expert committees of the Institute of Medicine (IOM), who base their decision upon an extensive review of the available scientific evidence. For calcium, the recommended intakes have been determined as those necessary to maintain calcium balance and bone health.1
The calcium requirements for the different age categories are listed in the table below. While recommendations may differ from country to country, the DRIs are fairly consistent with most national and international recommendations. For instance, the IOM’s calcium requirement for adults is 1,000 mg per day,2 which is similar to the World Health Organization’s (WHO) recommendation.3
|Recommended calcium intake, mg/day|
Note: Age cutoffs for each life stage differ slightly for the IOM vs. WHO.
Milk and milk products such as yogurt and cheese provide good amounts of calcium. Additionally, cow’s milk has good bioavailability, with a calcium absorption rate of about 30% to 35%.4
While certain dark green vegetables, such as broccoli and kale, have a higher absorption rate, they contain less calcium. To obtain the same amount of calcium found in one cup (1 serving) of milk, more than two cups (4 servings) of broccoli would have to be eaten.
Furthermore, the bioavailability of calcium from plant sources can be compromised by the presence of certain compounds. Some foods contain oxalic and phytic acids, which bind with calcium to form insoluble complexes and interfere with calcium absorption. These foods are considered to be poor sources of calcium.2
- Examples of foods with high levels of oxalic acid include spinach and rhubarb.
- Eating spinach at the same time as milk reduces the absorption of the calcium in the milk;5
- When assessing calcium intake, PEN (Practice-Based Evidence in Nutrition), the knowledge transfer tool developed by Dietitians of Canada indicates that calcium from spinach and rhubarb should not be included.6
- Examples of foods with high levels of phytic acid include wheat bran and whole-grain products, which are high in fibre.
- However, as the Canadian diet is generally low in dietary fibre, it is not recommended to limit the intake of phytic acid.6
As plant sources of calcium may be less bioavailable, they can be a barrier to adequate calcium intake. Therefore, diets consisting of only plant sources of calcium need to be evaluated for bioavailability.6
In conclusion, although milk and milk products are not the only source of calcium, consuming them as part of a healthy diet makes it easier to meet calcium requirements.
- Health Canada. 2012. Vitamin D and calcium: updated dietary reference intakes. www.hc-sc.gc.ca. Accessed July 17, 2015.
- Institute of Medicine. Dietary reference intakes for calcium and vitamin D. Washington, DC: The National Academies Press. 2010.
- World Health Organization and Food and Agricultural Organization of the United Nations. Vitamin and mineral requirements in human nutrition, second edition. 2004.
- Weaver CM and Plawecki KL. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr 1994;59:1238S-1241S.
- Heaney RP et al. Calcium absorbability from spinach. Am J Clin Nutr 1988;47:707-709.
- Practice-based Evidence in Nutrition. 2011. Should individuals with osteoporosis avoid dietary oxalates and phytates due to the effect on the absorption of calcium? www.pennutrition.com. Accessed July 17, 2015.