Few people perceive cola drinks as “healthy”, but while we suspect that they rot our teeth and expand our waistlines, bone weakness is not a consequence that springs to mind. Until now. A new study shows that for women and girls, drinking just four servings (ie, glasses, bottles or cans) a week of full-sugar or diet cola reduces bone density, which in turn can increase the chance of fractures whether you are aged 16 or 60.
The findings, published in The American Journal of Clinical Nutrition, were made by Katherine Tucker, of the Human Nutrition Research Centre on Ageing at Tufts University, Boston. She and her team compared the density of the hips and spines of 1,431 women over five years, at the end of which the heavier cola drinkers were found to have up to 5.4 per cent lower bone-mass density.
The premise is not a new one, but after previous studies cola manufacturers have always suggested that the results could be due to other factors — for example, the cola drinkers might be consuming less milk than others and therefore lack bone-building calcium. So Tucker’s researchers checked calcium and vitamin D intake, the amount of alcohol their subjects drank, whether they smoked, their use of oestrogen and whether they were pre or post-menopause (the women ranged in age from 29 to 83). Even the season was taken into account, as this can cause fluctuations in bone density.
Once the playing field had been levelled, the results were still clear. The hip bones of regular cola-drinkers had lower bone-mass density than those of non-cola drinkers.
“The main differences between cola and other carbonated beverages are caffeine, phosphoric acid and cola extract,” says Tucker. “Although caffeine probably contributes to lower bone-mass density, we found that the result stood for decaffeinated cola. So we put phosphoric acid — an additive that is put into cola to balance the flavour but is not present in other fizzy drinks — under scrutiny. We found that phosphoric acid in the digestive system may form a complex with dietary calcium to block its absorption, which would lower the amount of calcium available to bones.”
Research published in 1999 in the Journal of Clinical Epidemiology indicated that women who drank one cola drink a day had higher than normal levels of parathyroid hormone (PTH) in their blood. PTH activates bone-digesting cells which break down the bone matrix, releasing alkalising calcium into the blood. It has been suggested that this process may be triggered to help to rebalance the raised blood acidity potentially caused by phosphoric acid in cola beverages.
A reduced bone-mass density raises our risk of developing brittle bones and osteoporosis in later life. It is unclear why women and girls are more sensitive to the effects of cola than men, though it may be because they have smaller bones overall. Men and boys usually do more physical activity, too, which helps to build strong bones.
But when it comes to building bone health, for both sexes the situation is a lot more complex than whether you are a cola-guzzler. All 206 bones in our bodies are made up of a protein scaffold (mostly collagen) on to which hard minerals such as phosphorus, silicon, magnesium and calcium are deposited. However, both the framework and the minerals undergo continuous remodelling: every week we recycle between 5 and 7 per cent of our bone, and this process is influenced profoundly by what we eat and drink from day to day. Here are some of the minerals and foods we can consume that will help to build bone:
Calcium
Calcium is laid down on the protein superstructure of bone to give strength and resilience. The recommended intake is 700mg a day for women (600mg for men, 800mg for teenage girls and 1000mg for teenage boys). The National Osteoporosis Society and US guidelines recommend that we should consume 1200mg a day.
In the UK, both boys and girls fall below the national recommended intakes for those aged 11 to 18. Yet if young people get too little calcium, they start adult life with a deficit that makes eventual bone fractures more likely. You can consume 800mg of calcium a day by drinking a pint and a quarter of semi-skimmed or skimmed milk, or half a pint of calcium-enriched soya milk and a bowl of muesli, a handful of almonds, a yoghurt and two grilled sardines. Alternatively, try calcium supplements.
Vitamin D
Vitamin D carries calcium from our intestines into the blood. Although teenagers and adults are supposed to make enough vitamin D under their skin through the action of sunlight converting an inactive form of this vitamin into an active one, it does no harm to ensure that vitamin D-rich foods such as oily fish and eggs are on the menu regularly. Pregnant women and over-65s of both should take 10mcg daily.
Isoflavones
These supernutrients, found in soya milk, soya yoghurts and tofu, are associated with maintaining bone density post-menopausally through their ability to mimic oestrogen, a hormone needed for strong bones.
Prebiotics
A new and fascinating player in enhancing calcium absorption, prebiotics are types of fibre that feed probiotics, which are the good bacteria in our digestive tracts.
By nourishing probiotic bacteria, prebiotics improve gut health. Research from Baylor College of Medicine in Texas has revealed that raising prebiotic intakes can enhance our calcium absorption by 20 per cent, and as a result boost bone-mineral content by 15 per cent over the course of a year.
You can find prebiotics naturally as a type of fibre known as fructo-oligosaccharide in bananas, chicory, leeks, onions, whole-wheat foods, asparagus, peas, chickpeas and corn, but they are also being added to certain other foods such as Vogel’s UltraBran breakfast cereal (from Waitrose, Sainsbury’s and Holland & Barrett). Other prebiotic-rich products are bound to follow soon.
Vitamin K
Vitamin K activates proteins in our bones to grab hold of calcium. Vegetable oils are a major supplier, although the process of hardening them — and thereby turning them into trans fats — causes vitamin K to lose its bone-benefiting effects. Other good foods for vitamin K include dark green vegetables such as spinach and broccoli, and lettuce.
Silicon
Silicon, like calcium, is laid on to protein to harden bones. A nutrient, it is present in foods as forms of silica but there is no recommended daily amount. However, studies of pre-menopausal women have found that when their silica intake is greater than 30mg daily, bone-mineral density increases compared with intakes of 18mg and less.
Scientists from the MRC Human Nutrition Research Centre in Cambridge have found that women in the UK consume around 18mg of silica a day. Some of the best foods for it are French beans (with 8mg per average serving), porridge (7mg per bowl), oatcakes (5mg in every two), bananas and mangoes (also 5mg). Pineapples, sultanas, dates, marrows, spinach, tap water and tea are not bad, either.
Draught lager turns out to be exceptionally rich in silica (16mg per pint), and red and white wine contain 7mg per glass. Suddenly, bone-building seems a less daunting task.
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