Wednesday, 5 November 2014

Dairy Intake and Bone Strength - Caution May Be Needed

For a long time health experts have told us to eat lots of dairy foods in order to obtain enough calcium to build bones. Some alternate practitioners have claimed that dairy foods are harmful for health unless they're eaten in a fermented form. New research suggests that they may have a point.

A recent report in the British Medical Journal describes the results of a survey performed by Swedish researchers. The project involved 61,433 women and 45,339 men. The test subjects had a wide range of ages. The females were 39 to 74 years of age and the males were 45 to 79 years old. The subjects were asked to report how often they ate milk, cheese and yogurt. The health of the female participants was monitored for twenty years and that of the male participants for eleven years.

The researchers made some interesting discoveries about the participants in the study, including the following.
  • Women who drank more than three glasses of milk a day had a higher risk of bone fractures during the study period than those who drank either three or less than three glasses a day.
  • Women who drank three or more glasses of milk a day had twice the rate of death by the end of the study compared to those who drank less than one glass a day.
  • The results for men were similar to those of women but less pronounded.
  • The incidence of fractures or mortality were lower in both yogurt eaters and cheese eaters than in other subjects. In fact, the fermented foods appeared to improve health.

The research is definitely food for thought, but we need to be careful when we interpret the results. There is a common saying in science that "correlation does not equal causation". Just because there is a relationship between two factors doesn't necessarily mean that one factor is causing the other.

The conclusions in the study were based on questionnaires and surveys rather than on clinical tests. Clinical tests are generally considered to be more accurate than surveys. In addition, the females were asked about the amount of dairy that they ate only twice - once at the start of the study (1987-1990) and a second time in 1997. The males were only asked about their diet at the start of the study. Eating habits can change over the years. A third consideration is that factors such as lack of exercise, weight and alcohol consumption may have contributed to the study results, although the large number of people in the study may have overcome this influence.

The researchers recognize that the results of their study must be interpreted cautiously. However, they theorize that milk causes detrimental effects due to a sugar called D-galactose. This sugar is present in the lactose of milk and is released when our body breaks the lactose down. The researchers say that D-galactose has been shown to contribute to chronic inflammation and aging in lab animals. Interestingly, cheese and yogurt have much less lactose and galactose than milk.

I would love to see the results of a more rigorous research project that takes other factors into account in addition to dairy intake, such as the amount and type of exercise and the age of the participants. Bone strength is a very important health concern, especially as we age. We need to identify the factors that weaken bones and the ones that strengthen them.