This month’s edition of the American Journal of Clinical Nutrition has published a study which found that women drinking four or more cola drinks a week were at increased risk of reduced bone density (1). And this is not the first evidence that has linked the drinking of fizzy drinks to weaker bones. A number of explanations are generally put forward to attempt to explain this phenomenon. A constituent of cola is phosphoric acid, which is believed to impart a degree of acidity within the body that increases the risk that calcium is leeched from the bone. Caffeine, another common component in cola drinks, is also believed to stimulate calcium loss.
Another oft-quoted theory for how soft drinks can cause soft bone is that those who drink them are likely to drink less milk. That presupposes that milk is a great bone-builder, but it is it? I’ve attached a couple of articles here that examine the role of milk in bone health. The evidence suggests, that contrary to conventional wisdom, milk-drinking does not contribute significantly to bone health in women or children. The articles contain information about the factors that do seem to make a difference in this respect.
Observer Column – 23rd February 2003
The last couple of decades have seen doctors place increasing emphasis on the diagnosis and treatment of the thinning bone disease known as osteoporosis. Public awareness of this condition is so great, it seems that practically every middle-aged or elderly female patient I see in practice asks me about it, whatever their primary complaint. One of their particular concerns is whether they are drinking enough milk. Despite the conventional wisdom that the calcium in milk is good for bones, I’ve always found it curious that Asian women whose diets are often quite bereft of milk tend to have stronger bones compared to their milk-drinking Western counterparts. Recently, I thought I’d bone up on the research to see if drinking milk really does help to protect against osteoporosis.
Despite its rather inert image, bone is in fact in a state of constant renewal ” slowly but surely being broken down and built up again at about the same rate. Over time, if bone is undone more quickly than it is remade, then osteoporosis is the result. Osteoporosis is most common in women, particularly after the menopause when the bone-protective hormone oestrogen tends to be in short supply. The real risk for post-menopausal women is not the osteoporosis per se, but the fact that it increases the risk of potentially debilitating fractures such as those of the hip and the spine. Theoretically, feeding the bone with the nutrients that participate in its formation should help to stave off osteoporosis and reduce the risk of fracture.
As calcium is the predominant nutrient in bone, scientific eyes have traditionally focused on it as the major player in prevention of osteoporosis. Supplementation with calcium has indeed been shown to help bring small increases in bone density. Also, there is some research showing that drinking milk during childhood helps build better bones, and that the benefits may even persist into adulthood. However, the evidence that drinking milk in adulthood helps to strengthen bones is far weaker.
In a study published this month in the American Journal of Clinical Nutrition, researchers tracked the dietary habits and hip fracture rates in more than 72,000 women for 18 years (2). The results of this research found no relationship between the amount of milk and calcium women consume and their risk of fracture of the hip. In other words, drinking more milk does not seem to strengthen a woman’s bones. Much that this finding is somewhat counter-intuitive, it is not new: a previous review of the literature found that 12 of 14 studies examining the relationship between milk consumption and bone health found no association at all (3).
Women interested an alternative to cow’s milk might consider switching to soya milk. Soya is rich in oestrogen-like compounds called isoflavones that appear to help protect against osteoporosis. More than one study has found that increased soya consumption might actually increase bone density in time. Some scientists have suggested that the abundance of soya products in Asian women’s diets is a major reason for their apparent protection from osteoporosis. When mature female patients ask me about how to ward off osteoporosis, one suggestion I often give them is to use soya milk or soya yoghurt on their breakfast cereal in the morning, and maybe to add the occasional lump of tofu to a stir-fry or stew. I’m also keen to point out that the notion that drinking lots of dairy”derived milk is good for their bones looks like one sacred cow worth putting to rest.
Observer Column – 27th March 2005
I recently had Radio 4 on for a bit of oral wallpaper, and found my ears pricking up during an item on quangos. According to a recent report published by the Efficiency in Government Unit (EGU), the UK now has more than 500 of these ‘quasi-autonomous, non-governmental organisations’ which soak up billions of taxpayers pounds each year but often appear to offer dubious value for money. One quango rating highly in the ‘useless’ stakes in the EGU report is the Milk Development Council. At one point during the radio item, a representative from this organisation was heard hard-selling the healthy attributes of milk to school children. I was left wondering what merit there is in milking the benefits of a foodstuff that is generally taken to have a indispensable nutritional role in kids.
Those keen to tout the benefits of milk will often highlight the fact that it is a prime source of calcium for the building of bone in children. My experience in practice is that the belief that dairy-derived calcium is needed for strong and healthy bones is firmly entrenched in our psyches. This is evidenced by the fact that should I recommend the cutting out of milk and perhaps other dairy products from a child’s diet (usually because sensitivity to dairy foods is a frequent factor in health issues such as asthma, eczema and ear infections), parents will almost always express concern that this dietary change may leave their child short on calcium.
However, the tenet that dairy products are near-essential for bone-building in kids has been somewhat shattered on the publication of a study earlier this month in the journal Pediatrics (4). In it, American researchers cast a critical eye over the research assessing the role of calcium and dairy products in the bone health of children and young adults. Of 37 relevant studies, 27 found no relationship between dietary calcium or dairy product intake and measures of bone health. Of the remaining studies, any apparent benefit was surprisingly small.
While the bone benefits of calcium, including that derived from dairy products, may have been overstated, some of this nutrient is clearly essential for bone health. Good alternative sources of calcium include green leafy vegetables such as kale and broccoli. Veggies also tend to alkalinise the blood, something which appears to help preserve the calcium content of bone. Other good sources of calcium include tinned salmon and sardines. These are also rich in vitamin D – a nutrient that has an important role in the formation of healthy bone. Another lifestyle factor that has a bearing on the bones is exercise. Evidence suggests that activity during adolescence has a much greater influence on measures of bone health than calcium intake.
Although somewhat surprising, it seems the evidence suggests that bone health in kids has surprisingly little to do with the downing of dairy products. The authors of the study in Pediatrics conclude that the available evidence does not support the promotion of milk or other dairy products as bone builders in children and adolescents. Recent evidence appears to add some nutritional credence to the EGU’s recent branding of the Milk Development Council as one of the UK’s most useless quangos.
References:
1. Tucker KL, et al. Colas, but Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Stud. Am J Clin Nutr 2006;84(4):936-942
2. Feskanich D, et al. Calcium, vitamin D, milk consumption, and hip fractures: a prospective study among postmenopausal women. American Journal of Clinical Nutrition 2003 77(2):504-511
3. Weinsier RL, Krumdieck CL. Dairy foods and bone health: examination of the evidence. Am J Clin Nutr 2000;72:681″689
4. Lanou A J, et al. Calcium, dairy products, and bone health in children and young adults: a reevaluation of the evidence. Pediatrics. 2005 Mar;115(3):736-43
