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Calcium sources

From dairy to plants . . . what does the science say?

For decades, physicians, osteoporotic foundations, industries, and governments have advocated for calcium consumption to protect our bones, often emphasizing the necessity of dairy products to meet recommendations for musculoskeletal health (Weaver et al., 1999). However, recent research has called these recommendations into question.

While dairy products contain high concentrations of calcium, calcium absorption is largely effected by the combination of all available nutrients, such as sodium, animal protein, and potassium levels. Thus, analyzing the calcium content of a specific food is insufficient to determine its bioavailability. Sodium, for instance, enhances urinary calcium excretion, though increasing dietary potassium may counteract this (particularly in postmenopausal women) (Sellmeyer et al., 2002).

 

As plant foods are low in both sodium and animal protein, they actually perform better than their dairy counterparts. 40-64% of the calcium found in legumes and green vegetables may be absorbed, versus 32% of that found in dairy and 22% in dried white beans (Keller et al., 2002). After all, we consume food not nutrients - and a food is more than the sum of its parts!

 

So although the dairy industry wishes you to believe otherwise, fret not if you skip the milk. Plant-based sources may not only enhance bioavailability, but may also decrease the amount of calcium your body needs to maintain healthy bones!

WHAT TO BELIEVE

Calcium-rich Plants

It's easy to protect your bones while avoiding the harmful effects of animal products. In fact, 1 cup of cooked kale provides the same amount of absorbable calcium as 1 cup of cow's milk!

 

Here is a list of other plant foods to add to your fridge:

(UCSF Medical Center, 2017)

WHAT TO BELIEVE

The Effect of Animal Protein

How does the protein found in animal foods affect calcium absorption?

As animal protein is digested, it stimulates acid release from the stomach. To buffer this metabolic acid load, calcium is subsequently excreted. This exchange occurs positively and incrementally (Hegsted et al., 1981); the more animal protein consumed, the more calcium that is needed to neutralize the acid. In both human and rat studies, a direct, positive relationship has been demonstrated between casein consumption (a milk protein) and calcium excretion in the urine (Campbell and Campbell, 2005).

 

The osteoporotic effect of dairy products is therefore questionable. Whether the amount of calcium retained in the body overrides the amount excreted is controversial. Some research has documented a net calcium loss alongside animal protein consumption (Itoh et al., 1998), while other studies have indicated that bodily stores of calcium may not be affected by this excretion (Calvez et al., 2012) or may even improve (Thorpe and Evans, 2011).

Furthermore, countries with the greatest consumption of dairy products suffer the greatest burden of fractures (Hegsted, 1986). The per capita consumption of dairy in the United States, Australia, New Zealand, and Western Europe exceeds 300 kg per year. Simultaneously, the rate of hip fractures significantly surpasses Asian and African countries, where consumption ranges between 10 and 30 kg per year (Hegsted, 1986).

The relationship between animal protein consumption and urinary calcium excretion does not hold true for plant protein, however (Sellmeyer et al., 2001). Globally, the greater the ratio of animal protein to plant protein consumption, the greater the incidence of fractures. Just one more reason to follow a plant-based diet!

RECOMMENDED INTAKE

Recommended Daily Allowance

The USDA recommends the following for those consuming a standard American diet:

(UCSF Medical Center, 2017)

WHAT TO BELIEVE

The Role of Vitamin D

Calcitriol, the active form of vitamin D [1,25-Dihydroxyvitamin D or 1.25(OH)2D], plays a large role in serum calcium regulation. Through many complicated relationships with parathyroid hormone and serum phosphate, calcitriol directly effects calcium absorption and secretion (Breslau and Weinstock,1988). Populations living above 37 degrees or below -37 degrees latitude who face increased risk of vitamin D absorption also suffer from a greater risk of calcium deficiency (Harvard Medical School, 2008).

37 DEGREES LATITUDE

Photo taken from Michaels, A.M. (2017). Michaels has a blog entitled "Cheese Slave" that I do not endorse, however her above photo beatutifully depicts 37 degrees latitude.

37 DEGREES LATITUDE

Photo taken from Michaels, A.M. (2017). Michaels has a blog entitled "Cheese Slave" that I do not endorse, however her above photo beatutifully depicts 37 degrees latitude.

References

  1. UCSF Medical Center (2017). Calcium Content of Foods. University of California San Francisco Medical Center. Available from: https://www.ucsfhealth.org/education/calcium_content_of_selected_foods/ [Accessed 26 September, 2017].

  2. Weaver, C.M., Proulx, W.R. and Heaney, R. (1999). Choices for achieving adequate dietary calcium with a vegetarian diet. The American Journal of Clinical Nutrition, 70(3), 543s-548s.

  3. Sellmeyer, D.E., Schloetter, M. and Sebastian, A. (2002). Potassium citrate prevents increased urine calcium excretion and bone resorption induced by a high sodium chloride diet. The Journal of Clinical Endocrinology & Metabolism, 87(5), 2008-2012.

  4. Keller, J.L., Lanou, A.J. and Barnard, N (2002). The consumer cost of calcium from food and supplements. Journal of the American Dietetic Association, 102(11), 1669-1671.

  5. Hegsted, M., Schuette, S.A., Zemel, M.B. and Linkswiler, H.M. (1981). Urinary calcium and calcium balance in young men as affected by level of protein and phosphorus intake. Journal of Nutrition, 111(3), 553-562.

  6. Campbell, T.C. and Campbell, T.M. (2005). The china study: The most comprehensive study of nutrition ever conducted and the startling implications for diet, weight loss and long-term health. Dallas: Benbella Books.

  7. Itoh, R., Nishiyama, N. and Suyama, Y. (1998). Dietary protein intake and urinary excretion of calcium: A cross-sectional study in a healthy Japanese population. The American Journal of Clinical Nutrition, 67(3), 438-444.

  8. Calvez, J., Poupin, N., Chesneau, C., Lassale, C. and Tomé, D. (2012). Protein intake, calcium balance and health consequences. European Journal of Clinical Nutrition, 66(3), 281.

  9. Thorpe, M.P. and Evans, E.M. (2011). Dietary protein and bone health: armonizing conflicting theories. Nutrition Reviews, 69(4), 215-230.

  10. Hegsted, DM (1986). Calcium and Osteoporosis. Journal of Nutrition, 116, 2316-2319.

  11. Sellmeyer, D.E., Stone, K.L., Sebastian, A., Cummings, S.R., and the Study of Osteoporotic Fractures Research Group (2001). A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. The American Journal of Clinical Nutrition, 73(1), 118-122.

  12. Breslau, N.A. and Weinstock, R.S. (1988). Regulation of 1,25 (OH) 2D synthesis in hypoparathyroidism and pseudohypoparathyroidism. American Journal of Physiology-Endocrinology and Metabolism, 255(5), E730-E736.

  13. Harvard Medical School (2008). Time for more vitamin D. Harvard Health Publications. Available from http://www.health.harvard.edu/staying-healthy/time-for-more-vitamin-d [Accessed 7 March, 2017].

  14. Michaels, A.M. (2017). How to get enough Vitamin D (Especially in Winter). Cheese Slave. Available from: http://www.cheeseslave.com/about-me/ [Accessed 28 October, 2017].

Achieving health and happiness through evidence-based nutrition

 

Nikola Hamilton

MSc GLobal Public Health Nutrition

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Medical Disclaimer: The information provided on this site is intended for your general knowledge only and is not a substitute for professional medical advice or treatment for specific medical conditions. You should not use this information to diagnose or treat a health problem or disease without consulting with a qualified healthcare provider. Please consult your healthcare provider with any questions or concerns you may have regarding your condition. Furthermore, it is important to work closely with a qualified healthcare provider when starting any new exercise regimen, diet or treatment as dietary adjustments may alter medication needs or have other effects on physical health.