Dairy calcium intake does not protect people against osteoporosis (thin bones).
The dairy calcium story.
There are many factors associated with the development of osteoporosis. Here is a short list: white race, being female, family history, low weight at one year of age, poor intake or production of vitamin D, late menarche and/or early menopause, low levels of physical activity, certain diseases and drugs and so on (Jordan 02). Probably the biggest public health problem associated with osteoporosis is vitamin D deficiency. (See below) Lower dietary intake of calcium has been touted as a significant cause of osteoporosis but the evidence for this is very sparse.
The difficulties with calcium balance studies. Most studies are done are relatively short term in nature, over a few days or weeks. Hence they tend to reflect the background calcium intake. If a person consumes a high calcium diet, the balance studies will show a higher requirement for calcium. What has been established in the past is that balance studies done in people with a low intake of calcium show a much lower requirement (Hegsted 2000). The point is that the body responds very slowly over time to a lowered calcium intake taking months to set a new equilibrium. This was demonstrated in the 1950s by Malm in Sweden and seems overlooked in today's shorter term studies. Hence recommended daily intake levels of calcium tend to reflect the background level of calcium in that society since that is what the test subjects used for such balance studies are adapted to.
There is very little evidence to support the concept that higher calcium intakes make stronger bones. The most striking statistic is that countries such as the US and in northern Europe have high levels of osteoporotic fracture despite high intakes of dietary calcium (Hegsted 2000). In a recent European study (EPOS), fractures rates were in Scandinavia were the highest in Europe (Ismail 02). In a world wide assessment of hip fracture, the incidence in women at 80 years was around 500/100,000 in Latin America and Asia compared with around 2000 in Western Europe, but rising to between 3000 and 5000/100,000 in North American and North Europe (Gullberg 97).
The British Medical Journal recently published a meta analysis where the data from a large number of calcium supplementation trials were collated and reviewed. This showed no benefit from the extra calcium intake. It called into question the public health benefit of dairy supplementation on bone health in young people. In addition, there was no evidence that dairy calcium was superior to any other calcium source (Winzenberg 06). The most remarkable feature of this study was the widely varying baseline intake of calcium, with intakes 277mg/day up to 994mg/day across a number of ethnic groups. Calcium supplementation made little difference in bone mineral density in any of these groups from the lowest background intake to the highest.
This strongly suggests that bone health is not strongly related to calcium intake. Added to this was a similar study reported in 2005 in Pediatrics, the official journal of the American Academy of Pediatrics, which concluded that "Scant evidence supports nutrition guidelines focused specifically on increasing milk or other dairy product intake for promoting child and adolescent bone mineralization" (Lanou 05).
The problems with setting intake levels for calcium. In the most recent US National Academy of Sciences report on calcium and related nutrients (1997), there was disagreement over the interpretation of the data for calcium requirements such that only acceptable intake (AI) was set and that there were not enough data to set estimated average requirements (EARs) and hence recommended dietary allowances (RDAs) (National Academy 97).
One of the many problems has been the assumption that what is lost by the body can be assumed to be what the intake requirement should be allowing for differences in absorption of the calcium from different foods. This is a chicken-and-the-egg argument. The other way of looking at this is that the more that is consumed in excess of requirement, the more that is lost from the body. Hence calculations made on this basis reflect the background intake of calcium rather than the long term requirement. As noted by Hegsted, many of the calcium studies have been done only over short periods of days to weeks, where as more meaningful results would be gained from much longer term studies which are much more difficult to do (Hegsted 00).These have not been done so far.
Finally the information gained from clinical trials of calcium supplementation as noted above, by and large, do not give answers as to what intakes should be set at as supplementation appears to lack benefit. There has been a general lack of concordance between such observational studies and the experimental data.
Does cow's milk prevent osteoporosis? The fairly clear answer to this, derived from many sources, is no. First, a large observational study in the US showed if anything an increased rate of osteoporosis with increasing milk consumption. In a 12 year prospective study of just under 78,000 women who had not used calcium supplements, those who drank two or more glasses per day had a relative risk of hip fracture of 1.45 compared to those consuming one or less glasses per day. Further when total dietary calcium was assessed, higher calcium intakes were not associated with a reduced rate of fractures (Feskanich 97).
Is cow's milk an ideal food? This idea has been put forward by the dairy industry for years and it is a deeply ingrained view by many people. However, is milk an ideal food? The short answer is no. Cow's milk is unsuitable for children less than one year old because of its composition which is very different to human milk:
Too much dairy in very young children is a leading cause of iron deficiency as noted in a recent UK study. The other factor of milk is that it is relatively high in protein. As noted elsewhere, most western diets contain an excess of protein a probably major driver of osteoporosis. There is no advantage what-so-ever in a high protein diet for anyone, the excess is simply burned as energy. High protein diets don't give big muscles but the saturated fat associated with much of animal-based foods will make you fat. Milk is a good example of this.
Dairy foods are not health foods, quite the reverse. The reality is that it is actually difficult to find studies that support the use of dairy foods as being good for you. There is a huge body of literature that shows that there is no effect no effect on osteoporosis. This would not be a problem if it were not for the fact that dairy foods contain significant levels of very harmful saturated animal fat which add greatly to energy intake and damage arteries. Despite the fact that the dairy producers market milk as a health food, there is very little to recommend dairy products as staple foods: dairy is not health food and should only be consumed in limited amounts.
Do vegetarians have a problem with osteoporosis? In lacto-ovo-vegetarians (the ones that consume eggs and dairy products) calcium intakes are similar to those in omnivores.(National Academy 97) There is no evidence of clinically significant osteoporosis in vegetarians, although bone mineral density has been shown to be marginally lowered especially in vegans. However, this reduction is not clinically significant. (Ho-Pham 09)
The role of other foods in the osteoporosis story: cola, other soft drinks, caffeine are not implicated. The cola drink story is often quoted because of the presence of phosphoric acid which potentially could interfere with calcium metabolism. This has been disproved. Excessive consumption of other types of soft drinks could also be implicated. High sugar intake can increase calcium loss but this effect is not maintained. A more likely possibility is the displacement of calcium rich foods such as milk, with soft drink being consumed in preference. However, if calcium intake is adequate from other sources in the diet, this should not be a problem. Caffeine has also been nominated. Again in the short term, there is a flux of calcium loss in the urine initially but this is corrected subsequently, so that overall there is no excess calcium loss (Fitzpatrick 03).
(Feskanich 97) Diane Feskanich, Walter C. Willett, MeirJ. Stampfer, Graham A. Colditz. Milk. Dietary Calcium, and Bone Fractures in Women: A 12-Year Prospective Study. American Journal of Public Health l997; 87:992-998
(Fitzpatrick 03) Lorraine Fitzpatrick, Robert Heaney. Got Soda? Journal of Bone and Mineral Research. 2003;18:1570-1571.
(Gullberg 97) B. Gullberg, O. Johnell and J. A. Kanis. World-wide Projections for Hip Fracture. Osteoporos Int (1997) 7:407–413
(Hegsted 00) D. M. Hegsted. From Chick Nutrition to Nutrition Policy. Ann. Rev. Nutr. 2000;20:1-19
(Ho-Pham 09) Lan T Ho-Pham, Nguyen D Nguyen, Tuan V Nguyen. Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis. Am J Clin Nut 2009; 90:1-8.
(Ismail 02) Ismail AA et al. Incidence of Limb Fracture across Europe: Results from the European Prospective Osteoporosis Study (EPOS). Osteoporos Int 2002;13:565–571
(Jordan 02) K M Jordan, C. Cooper. Epidemiology of osteoporosis. Best Practice and Research Clinical Rheumatology 2002;16: 795-806.
(Lanou 05) Amy Joy Lanou, Susan E. Berkow, Neal D. Barnard. Calcium, Dairy Products, and Bone Health in Children and Young Adults: A Reevaluation of the Evidence. Pediatrics 2005;115:736-743
(National Academy 97) Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. National Academy Press 1997.
(Newmark 04) Harold L Newmark, Robert P Heaney, Paul A Lachance. Should calcium and vitamin D be added to the current enrichment program for cereal-grain products? Am J Clin Nutr 2004;80:264–70.
(Winzenberg 06) Tania Winzenberg, Kelly Shaw, Jayne Fryer, Graeme Jones. Effects of calcium supplementation on bone density in healthy children: meta-analysis of randomised controlled trials. BMJ 2006 doi:10.1136/bmj.38950.561400.55