Can we use calcium from dairy products?

A few weeks ago when I entered Aunt Gayle’s hospice room, the gathered family had a nutrition question for me: can humans absorb the calcium found in milk and other dairy products? I was fairly confident that dairy is a good source of calcium and is well absorbed. If not, the government and the dairy industry’s been doing us a huge disservice for decades.

Then my mother-in-law raised the same question this weekend. Her doctor had recommended leafy greens as a calcium source. Again, I was fairly confident that most leafy greens are a good source of calcium, though not necessarily as well absorbed.

So what's the deal? Should one consume dairy products for the calcium? My newly purchased textbook, Krause’s Food and Nutrition Therapy, by L. Kathleen Mahan and Sylvia Escott-Stump (Saunders-Elsevier, 2008), offers two reasons to do so. First, dairy products are the most concentrated calcium sources, and second, lactose enhances calcium absorption, probably even in those with lactose intolerance (104, 106).

A cursory glance at a Google Scholar search related to lactose-enhanced calcium absorption reassured me that this reason was probably valid.And while "most concentrated" sounded about right, I was curious as to how exactly that played out.

I started calculating the concentration of calcium in some foods, both dairy and non-dairy to get some numbers. I began by calculating milligrams of calcium per calorie, but that didn’t result in dairy being uniformly more concentrated:

Food	Calcium (mg)	Kcals	Mg Ca per kcal
Yogurt, plain, low fat, 1 cup (245g)	448	154	2.9
Milk, 2%, 1 cup (144g)	286	122	2.3
Cheddar cheese, 1 oz (28g)	202	113	1.8
¼ block firm tofu (81g)	163	57	2.9
Kale, 1 cup cooked (130g)	94	36	2.6
Broccoli, 1 cup cooked (156g)	62	54	1.2
Almonds, 1 oz (28g)	75	169	0.4

Tofu stands eye-to-eye with yogurt, a cup of kale beats a cup of milk - what's going on? I switched to milligrams of calcium per gram, which still didn’t yield the results I expected:

Food	Mg Ca per gram
Cheddar cheese, 1 oz	7.2
Yogurt, plain, low fat, 8 oz	1.8
Milk, 2%, 1 cup	1.2
Almonds, 1 oz	2.7
¼ block firm tofu	2.0
Kale, 1 cup cooked	0.7
Broccoli, 1 cup cooked	0.4

Here, water content plays a big role - generally the more water, the heavier the food is. Cheddar is the leader by far, since cheese is basically milk wrung of water. This time, almonds are doing pretty well, and tofu is still a champ. NOTE: These calculations are based on calcium-set tofu, not the silken type, which has about 80% less calcium. Straight-up cooked soybeans have about 0.6 mg Ca per kcal, and 1.0 mg per gram.

Bottom line – the author of the statement "Cow's milk is and dairy products are the most concentrated sources of calcium" has a different understanding of “concentrated sources” than I do.

Next up: the relationship between protein and calcium.

Photo Source: UMN Extension