Soy vs. Cow’s Milk and Bone Mineral Density
I’m going through my backlog of research on bones in order to write a reader-friendly version of the tome that is Bones, Vitamin D, and Calcium on VeganHealth.org.
In January 2012, a report from China was released of a randomized clinical trial comparing the effects of cow’s milk and soymilk on bone mineral density (BMD) in postmenopausal women (1).
The women were divided into three groups: soy, cow’s, and control. The women knew which treatment they were receiving, while the control group got nothing. The milk and soymilk had 250 mg of calcium and they drank one serving per day.
BMD was measured in the spine, hip, and femur at 6, 12, and 18 months.
In the cow’s milk group, BMD increased in the hip and femur. In the soymilk group, BMD did not change significantly, but showed a downward trend in all three locations. In the control group, there was a downward trend in all three locations that only reached significance in the femur at 18 months.
It should be strongly noted that the participants were asked to avoid calcium from other milks and supplements during the trial which means their total calcium intake was probably quite low and I’m somewhat amazed that their BMD didn’t decrease more or in all three groups. Total calcium intake during the study period was not reported.
Compliance was 93.1% in the cow’s milk group and 82.5% in the soymilk group. This might explain a small amount of the differences between those groups. Other possibilities are that calcium in fortified soymilk is known to quickly settle to the bottom of the milk where it might not be ingested but left in the container, and that milk contains phosphorus and growth factors that might increase BMD.
This is just one small study and more work needs to be done before any conclusions should be drawn.
1. Gui JC, Brašić JR, Liu XD, Gong GY, Zhang GM, Liu CJ, Gao GQ. Bone mineral density in postmenopausal Chinese women treated with calcium fortification in soymilk and cow’s milk. Osteoporos Int. 2012 May;23(5):1563-70. Epub 2012 Jan 27. | link