Osteoporosis

Osteoporosis

Bones consist of a thick outer shell and a strong inner mesh filled with a protein called collagen, calcium salts and other minerals. Osteoporosis (meaning porous bones) occurs when calcium is lost from the bones and they become more fragile and prone to fracture. This debilitating condition tends to occur mostly in postmenopausal women due to a lack of the hormone oestrogen, which helps to regulate the incorporation of calcium into the bones. Osteoporosis tends to occur mostly among postmenopausal women aged between 51 and 75. It can occur earlier or later and not all women are at equal risk of developing osteoporosis.

Osteoporosis is sometimes called the silent disease as there are often no symptoms until a fracture occurs. Although the whole skeleton is usually affected, fractures mostly occur in the wrist, spine and hip. One in two women and one in five men in the UK will suffer a fracture after the age of 50; in fact every three minutes someone has a fracture due to osteoporosis (National Osteoporosis Society, 2005). However, osteoporosis has been diagnosed in people as young as 20. The dairy industry has responded to this health scare by promoting the consumption of milk, cheese and yogurt directly to teenage girls in a campaign run by the Milk Development Council (MDC, 2005a).

It is deeply entrenched in the British psyche that calcium from dairy sources is essential for good bone health. However, a recent review on dairy products and bone health published in the official journal of the American Academy of Pediatrics challenged this misleading notion by concluding that there is very little evidence to support increasing the consumption of dairy products in children and young adults in order to promote bone health (Lanou et al., 2005). This review examined the effects of dairy products and total dietary calcium on bone integrity in children and young adults and found that out of 37 studies, 27 showed no relationship between dairy or dietary calcium intake and measures of bone health. In the remaining studies the effects on bone health were either small or results were confounded by the fortification of milk with vitamin D.

American women are among the biggest consumers of calcium in the world, yet they have one of the highest levels of osteoporosis (Frassetto et al., 2000). African Bantu women, on the other hand, eat almost no dairy products at all; they have a relatively low calcium intake, mainly from vegetable sources, and typically have up to 10 children each. Yet osteoporosis is virtually unknown among Bantu women (Walker et al., 1972).

It seems that the more dairy produce we consume, the higher our risk of fracture. The Harvard Nurses Health study examined whether higher intakes of milk can reduce the risk of osteoporotic fractures. The study observed over 75,000 women for 12 years and concluded that increasing milk consumption did not confer a protective effect against hip or forearm fracture (Feskanich et al., 1997). In fact the report suggested that an increased calcium intake from dairy foods was associated with a higher risk of fracture.  

It has been suggested that calcium loss from the bone is promoted by a high intake of animal protein. One study of 1,600 older women examined the level of bone loss and found vegetarians had only 18 per cent less bone mineral compared to omnivores who had lost 35 per cent bone mineral by the age of 80 (Marsh et al., 1988). Another study of 1,035 elderly women found that women with a high ratio of animal to vegetable protein intake had a greater risk of hip fracture than those with a low ratio (Sellmeyer et al., 2001). In a similar study that analysed the incidence of hip fracture in relation to the consumption of animal and vegetable protein in 33 countries, it was concluded that moderating the consumption of animal food might protect against hip fracture (Frassetto et al., 2000). Cross-cultural studies summarising data on protein intake and fracture rates from 16 countries compared industrialised and non-industrialised lifestyles and revealed strong links between a high animal protein diet, bone degeneration and the occurrence of hip fractures (Abelow et al., 1992). In the book The China Study, Campbell observed that in rural communities where animal protein made up just 10 per cent of the total protein intake (the other 90 per cent coming from plant-based sources) the bone fracture rate was one-fifth of that in the US where 50 per cent or more of total protein is made up of animal protein (Campbell and Campbell, 2005), again indicating a link between animal protein and bone degeneration.

But what is the mechanism for this process? As food is digested acids are released into the blood, and the body attempts to neutralise the acid by drawing calcium from the bones. This calcium is then excreted in the urine (the calciuric response). Animal protein from cow’s milk and dairy products as well as meat, fish and eggs has a particularly bad effect because of the greater amount of sulphur-containing amino acids it contains compared to plant protein. As the sulphur content of the diet increases so does the level of calcium in the urine. Studies reveal that an animal protein diet (with the same total quantity of protein as a vegetarian diet) confers an increased risk for uric acid stones (Breslau et al., 1988). Furthermore the animal-protein induced calciuric response may be a risk factor for the development of osteoporosis. The traditional Inuit (or Eskimo) diet is made up almost entirely of animal protein. Inuits potentially have one of the highest calcium intakes in the world (up to 2,500 milligrams per day) depending on whether they eat whole fish, including the bones, or not. They also have a high rate of osteoporosis, even higher than white Americans (Mazess et al., 1974; Mazess et al., 1975; Pratt et al., 2001).

There are many factors linked to bone health that may even be more important than calcium. For example, when the bone density of 80 young women was monitored over a 10-year period, it showed that exercise was more important than calcium intake (Lloyd et al., 2004). In older people, a 15-year investigation into whether low calcium intake was a risk factor for hip fractures concluded that cutting back on dairy did not increase the risk and that physical activity provided better protection (Wickham et al., 1989). The discovery of 18th-century human bones under a London church revealed that today’s women lose far more calcium than our ancestors (Lees et al., 1993). This may be attributed to a lower degree of physical activity. This research supports an increasing amount of evidence that physical activity is a key factor in reducing osteoporosis risk. 

An increasing amount of evidence now shows that milk is not the best source of calcium at all and suggests that our bone health would benefit enormously if we switched to plant-based sources. Interestingly, a large share of the calcium in our diets (over 50 per cent) comes from sources other than dairy foods (FSA, 2003b). This is not surprising as most people in the world (over 70 per cent) obtain their calcium from plant-based sources rather than dairy products. Good plant-based sources of calcium include non-oxalate (eg spinach) dark green leafy vegetables such as broccoli, kale, spring greens, cabbage, bok choy and watercress. Also rich in calcium are dried fruits, such as figs and dates, nuts, particularly almonds and brazil nuts, and seeds including sesame seeds and tahini (sesame seed paste) which contains a massive 680mg of calcium per 100g. Pulses including soya beans, kidney beans, chick peas, baked beans, broad beans, lentils, peas and calcium-set tofu (soya bean curd) provide a good source of calcium. A good additional source is calcium-enriched soya milk. Interestingly, the calcium in dairy products is not as well absorbed as that in many dark green leafy vegetables, for example, in one study calcium absorbability from kale was demonstrated to be considerably higher than that from cow’s milk (Heaney and Weaver, 1990).

In summary, research suggests that physical (especially weight-bearing) exercise is the most critical factor for maintaining healthy bones, followed by improving the diet and lifestyle; this means eating plenty of fresh fruit and vegetables, and cutting down on caffeine and avoiding alcohol and smoking.