Investing in Nutrient Dense Foods: Calcium
This post’s focus is on calcium, the single most abundant mineral in the human body. Calcium plays many roles in our bodies, including supporting the proper function of muscles, nerves and muscled organs like the heart, as well as providing some of the mineral structure that underlies the strength and resilience of bone and teeth . Interestingly enough, the concentration of calcium in our blood doesn't vary all that much; our bones and teeth are used as reservoirs of calcium, and the mineral is removed from and redeposited to these stores as needed .
One interesting fact I uncovered in doing research for this post is that consuming lots of calcium won’t necessarily build strong bones; the body must sense the need for additional bone mass, necessitating an active lifestyle for calcium to be absorbed from food and purposed towards building bones and teeth. As many know, Vitamin D plays a vital role supporting the body's absorption of calcium as does magnesium, so those with chronic deficiencies of these nutrients may struggle to maintain adequate stores of the mineral.
We can get calcium from a range of foods, including dairy products like milk and cheese, deep green leafy vegetables like kale and cabbage, as well as broths made from the bones of animals like cows and chickens. The following graph shows the cost associated with consuming a daily allowance of 1,000 mg of calcium from a range of different foods. Calcium contents for these foods were sourced from the USDA's National Nutrient Database, while costs were recorded at my local farmers' market or grocery cooperative and reflect prices for grass fed or pastured animal products and certified organic produce .
The milk price used for the above graph was $10 per gallon, which is what it costs me to source 100% grass fed milk from a local raw dairy, while the price I used for cheese was $15 per pound, which is what I pay for cheddar cheese made from unpasteurized milk. Despite these high prices, milk and cheddar cheese still represent the most cost-effective sources of calcium, followed by the green leafy vegetables cabbage, spinach and kale. It's worth noting there's an inverse relationship between a vegetable's oxalic acid content and the absorbability of its calcium, so spinach, while calcium rich, might not be a particularly good source of the mineral because of its high oxalic acid content . This is the only graph presented so far where organ meats didn't feature prominently among cost-effective sources of a nutrient, and my guess is the only reason pork made the graph is because the cut I gathered data on was cooked bone-in and some of the calcium leached into the meat during the cooking process.
Bone broth is likely also a good source of calcium, although I wasn't able to find any research articles quantifying levels of calcium in the broth nor have I ever seen bone broth available commercially so that I can figure it's price. Bone broth is easy enough to make, simply buy bones - often marketed as marrow bones or soup bones - from animals like cows, goats or sheep or from a whole chicken, immerse them in water and simmer ever so gently for a few, or even several, hours. One article I did find suggested that the concentration of calcium in bone broth water stabilizes after about an hour, suggesting little value in cooking bone broth for hours or days, at least as far as calcium leaching goes . The study also found no evidence that adding vinegar to bone broths aided the extraction of calcium into solution. Regardless, I drink a fair amount of home made bone broth, and find it to be quite nourishing.
Calcium absorption, bioavailability and bioconversion is a hugely complex topic, one I can't remotely do justice to in this short blog post. One point I uncovered worth finishing this post with is that prebiotics - among them inulin - seem to enhance calcium absorption from plant foods [6, 7]. Inulin, as some may know, is a type of soluble fiber often termed resistant starch, a hot topic in health circles these days as people gain a better appreciation for the value it adds to diets. On a personal level, I'm banking on my modest consumption of raw dairy products, bone broth, leafy green vegetables and prebiotics to provide adequate calcium intake.
- Calcium and Bone Health. Centers for Disease Control and Prevention, United States Department of Health and Human Services.
- Calcium Dietary Fact Sheet. National Institutes of Heath, United States Department of Health and Human Services.
- National Nutrient Database for Standard Reference. United States Department of Agriculture, Agricultural Research Service.
- C. Weaver, et al (1997) Calcium bioavailability from high oxalate vegetables: Chinese vegetables, sweet potatoes and rhubarb. Journal of Food Science, Vol. 62, Pgs. 524-525.
- R. McCance (1934) Bone and vegetable broth. Archives of Disease in Childhood, Vol. 9, Pgs. 251-258.
- K. Kashman (2002) Calcium intake, calcium bioavailability and bone health. British Journal of Nutrition, Vol. 87, Pgs. S169-S177.
- K. Kashman (2003) Prebiotics and calcium bioavailability. Current Issues in Intestinal Microbiology, Vol. 4, Pgs. 21-32.
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