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Osteoporosis (meaning porous bones) is a condition that affects the bones, causing them to become weak and more likely to fracture. Although the whole skeleton is usually affected, fractures most commonly occur in the spine, wrist and hips. Osteoporosis is sometimes called the silent disease as there are often no symptoms until a fracture occurs.
Bones consist of a thick outer shell and a strong inner mesh filled with a protein called collagen, calcium salts and other minerals. Osteoporosis 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 between 51 and 75 due to a lack of the hormone oestrogen, which helps to regulate the incorporation of calcium into the bones. It can occur earlier or later and not all women are at equal risk of developing osteoporosis. Around three million people in the UK are thought to have osteoporosis and there are over 250,000 fractures every year as a result. Although commonly associated with post-menopausal women, osteoporosis can also affect men, younger women and children. In the UK, one in two women and one in five men over the age of 50 will break a bone mainly because of poor bone health.
In 2006, the dairy industry responded to this health scare by promoting milk, cheese and yogurt directly to teenage girls in an advertising campaign called Naturally Beautiful, run by the Milk Development Council with the support from the European Commission. Since then, the promoting of cow’s milk and cheese to teenage girls for bone health has decreased. DairyCo now tends to focus more on promoting milk in schools by providing ‘educational resources’ and website material for schools as well as promoting dairy farming actively to the public through their consumer facing website as well as talking to the media. Most people know about osteoporosis and it is commonly assumed that dairy products can help protect against it. This association is more to do with successful marketing than scientific evidence.
In 2012, researchers from The WHO Collaborating Centre for Metabolic Bone Diseases, at the University of Sheffield Medical School in the UK published a review of hip fracture incidence and probability of fracture worldwide. The graph shows the hip fracture rates for women per 100,000 from a range of countries. The pattern for men was broadly similar to that for women. The authors of this review observed a greater than 10-fold variation in hip fracture risk between countries. The high-risk countries extended from North Western Europe (Iceland, UK, Ireland, Denmark, Sweden and Norway) through central Europe (Belgium, Germany, Austria, Switzerland and Italy) to the south west (Greece, Hungary, Czech Republic, Slovakia, Slovenia) and onwards (to the Lebanon, Oman and Iran). Other high-risk countries for women were Hong Kong, Singapore, Malta and Taiwan. Notably, if ethnic-specific rates were considered in the US, then Hispanic, Asian and Black populations (often lactose intolerant and so non-milk consumers) would be described as low risk but Caucasian women were deemed to be at a high risk (this is why the US appears in the middle of the graph). Regions of moderate risk included Oceania (a region centred on the islands of the tropical Pacific Ocean), the Russian Federation, the southern countries of Latin America and the countries of North America. Low-risk regions included the northern regions of Latin America, Africa, Jordan and Saudi Arabia, India, China, Indonesia and the Philippines. In Europe, the majority of countries were categorised at high or moderate risk with the exceptions of Croatia and Romania. In summary, fracture rates are highest in Caucasian women living in temperate climates and are somewhat lower in women from Mediterranean and Asian countries and are lowest among women in Africa. Countries in economic transition, such as Hong Kong, have seen significant increases in fracture rates in recent decades. This indicates that environmental factors, such as diet, are responsible.
In their recommendations for preventing osteoporosis the WHO state that:
“With regard to calcium intakes to prevent osteoporosis, the Consultation referred to the recommendations of the Joint FAO/WHO Expert Consultation on Vitamin and Mineral Requirements in Human Nutrition which highlighted the calcium paradox. The paradox (that hip fracture rates are higher in developed countries where calcium intake is higher than in developing countries where calcium intake is lower) clearly calls for an explanation. To date, the accumulated data indicate that the adverse effect of protein, in particular animal (but not vegetable) protein, might outweigh the positive effect of calcium intake on calcium balance.”
It is deeply entrenched in the British psyche that calcium from dairy sources is essential for good bone health. However, a 2005 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. 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. The following year, a meta-analysis of 19 studies involving 2,859 children, published in the British Medical Journal found that calcium supplementation in children was unlikely to decrease the risk of fracture in childhood or in later life. This research strengthens previous evidence that calcium or and/or dairy products do not have a clinically relevant impact on bone health in youth. More recently, a prospective study involving 61,433 Swedish women followed over 19 years, investigated associations between the long-term dietary intake of calcium and risk of fracture and osteoporosis. The findings did show an association between very low dietary calcium intake and an increased risk of fractures but above this base level of just 750mg, increased intakes of calcium were not associated a reduction in risk of fracture or osteoporosis. In addition to that, the rate of hip fracture was actually increased in those with high dietary calcium intakes. For adults over 50, the recommended daily intake in the UK is 700mg per day and in the US it is 1,200mg per day.
The graph above supports earlier research that shows how Western style diets (rich in dairy foods and animal protein) accompany hip fracture rates around the world. A study, looking at hip fracture incidence in 33 different countries in relation to consumption of vegetable and animal protein, found that the countries with the lowest fracture rates also had the lowest intakes of animal protein. Conversely, in 10 of the 11 countries with the highest fracture rates, animal protein intake exceeded vegetable protein intake. The authors say that hip fracture incidence is directly related to animal protein intake and suggest that bone integrity is compromised by endogenous acid production that results from the metabolism of animal proteins. They suggest that the moderation of animal food intake, coupled to an increased ratio of vegetable to animal food consumption, may confer a protective effect. Another study of 757 young girls in urban Beijing in China, compared the effects of protein intakes from animal and plant sources on bone mass accrual over five years. Results showed that protein from animal foods, particularly meat, had negative effects on bone mineral content. It was concluded that higher protein intake, especially from animal foods, has a significant negative effect on bone mass accrual in pre-pubertal girls.
Other studies link animal protein to a decrease in bone mineral density. One study compared the effects of animal and plant-based protein in the diets of overweight and obese post-menopausal women dieting. They found that the energy-restricted diet with protein from meat sources promoted bone loss compared with an energy-restricted diet without meat. They concluded that for post-menopausal women, choosing a diet containing meat may decrease bone mineral density and increase the risk of osteoporosis. This extends the findings of an earlier study which examined the levels of bone loss in 1,600 older women and found that vegetarians had lost only 18 per cent bone mineral compared to omnivores who had lost 35 per cent bone mineral by the age of 80. 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. 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. 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, again indicating a link between animal protein and bone degeneration.
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. In fact the report suggested that an increased calcium intake from dairy foods was associated with a higher risk of fracture. They concluded that their results do not support the hypothesis that higher consumption of milk or other food sources of calcium by adult women protects against hip or forearm fractures. In a more recent extensive review of studies looking at total calcium intake and hip fracture risk, results showed that in prospective cohort studies, calcium intake was not significantly associated with hip fracture risk in women or men. The pooled results from randomised controlled trials not only found no reduction in hip fracture risk with calcium supplementation but suggested an increased risk with calcium supplementation among men and women.
But if animal protein is to blame, 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. 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.
So, for children and adolescents, while an adequate intake of protein is necessary for good bone development and stability, animal protein can counter this positive effect by increasing the dietary acid load, leading to bone demineralisation. In a study looking at long-term dietary protein intake, dietary acid load and bone status in children, it was concluded that the positive effect of protein could be negated, at least partly, by a high renal acid load. The authors say that their findings support the health benefit of a diet rich in base-yielding fruit and vegetables (which is in accordance with the 5-a-day campaign) and recommend an integrative approach saying that focusing on single nutrients is not sufficient.
Indeed, there are many factors linked to bone health that may even be more important than calcium. For example, some studies show that exercise is the predominant lifestyle determinant of bone strength. 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. In a group of 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. The discovery of 18th-century human bones under a London church revealed that today’s women lose far more calcium than our ancestors. 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.
Other studies suggest a detrimental effect of dietary salt (sodium chloride) on bone health. One study describes how a typical American diet contains amounts of sodium chloride far above evolutionary norms and potassium levels far below. This imbalance is thought to contribute to the acid producing effects of a typical Western diet. This may contribute to development of osteoporosis, kidney stones and other health problems. The authors point out how, after seven million years of hominid evolution, humans remain genetically adapted to the potassium-rich, sodium-chloride-poor, net base-producing diet of our ancestral hunter-gatherers. In other words, our bodies are not well-suited to an acid-producing diet. The shift to the contemporary diet occurred too recently for evolutionary forces to have had the opportunity to make any changes in our metabolic machinery. However, they suggest that decreasing salt intake and increasing the intake of plant foods may not just help the aging skeleton but provide other potential health benefits as well.
Other studies suggest a positive role in bone health for vitamin K. A review of projects funded by the UK Food Standards Agency examined the potential benefits of fruit and vegetables, vitamin K, early-life nutrition and vitamin D on bone health. They reached two conclusions; firstly that a diet rich in fruit and vegetables might be beneficial to bone health and secondly that an increased consumption of vitamin K may also contribute to bone health. A major research gap they identified was the need to investigate vitamin D status in relation to bone health in different groups. A higher calcium intake is still the primary recommendation for the prevention of osteoporosis, and vitamin D deficiency is often overlooked. In a study of US adults, a large proportion of younger and older adults were found to be below the desirable vitamin D threshold, whereas calcium intakes seemed to be adequate in the majority of individuals. The authors concluded that the correction of Vitamin D status is more important than increasing dietary calcium intake.
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, the 2003 National Diet and Nutrition Survey showed that a large share of the calcium in our diets (over 50 per cent) comes from sources other than dairy foods. 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.
The interaction between calcium intake and physical activity, sun exposure and intake of other dietary components (vitamin D, vitamin K, sodium, protein) and protective phytonutrients (soya compounds), needs to be considered before recommending increased calcium intake in countries with low fracture incidence. In a recent paper in the British Medical Journal, Dr Amy Lanou suggests that it is time to revise our calcium recommendations for young people and change our assumptions about the role of calcium, milk and other dairy products in the bone health of children and adolescents. Lanou argues that while the policy experts work on revising recommendations, doctors and other health professionals should encourage children to spend time in active play or sports and to consume a nutritious diet built from whole foods from plant sources to achieve and maintain a healthy weight and provide an environment conducive to building strong bones. 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.
For references, please see the White Lies report.
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