As people are living longer, scientists are determined to conquer one of the commonest conditions of old age: fragile bones. But it’s proving a tough problem to crack. This latest study – the largest of its kind – suggests that the answer does not lie in drinking copious amounts of milk, or scoffing chunks of cheese.
Instead, we must look to a more holistic approach, the authors conclude – perhaps to other dairy products and how they may interact with the rest of our diet to protect our bones.
As we get older, bone loss due to osteoporosis puts us at risk of painful and disabling breaks. And with an estimated one in three women and one in five men over the age of 50 years suffering an osteoporotic fracture, the condition places a heavy burden on our global society.
We know that milk and other dairy products, such as yogurt and cheese, can provide us with the right cocktail of nutrients – calcium, vitamin D (in fortified products), and protein – needed to keep our bones healthy. But so far studies haven’t told us whether drinking milk, for example, can actually prevent bone breakages. That’s at least partly because it’s too much to expect people to stick to restrictions in their diet for the long periods that are needed in such studies. And the studies that have been carried out have given inconsistent results.
Lactose intolerance: an unexpected source of help
So how do we solve this conundrum? It may sound strange, but some important clues are coming from a certain group of people who have a genetically-determined difficulty in digesting milk. The predominant sugar in milk – lactose – is broken down in the gut by the enzyme lactase. Whereas most people in Northern Europe continue to produce lactase throughout life, those who have ‘lactase non-persistence’ show a decline in the enzyme. For them, drinking milk can spell a digestive disaster, triggering symptoms of lactose intolerance such as stomach aches and diarrhoea.
So it comes as no surprise that people with this genetic trait aren’t exactly queuing up to buy their bottle of milk. And if they’re avoiding milk because it makes them ill, it stands to reason that studying bone health in this group is a sure-fire way to get a more accurate picture than studies that rely on diet changes.
Relating milk intake to risk of broken bones
People with lactase non-persistence might be expected to have weaker bones and be more prone to breaking their bones. Hence the authors of this article looked at the links between milk intake, lactase persistence (shown by genetic testing), and risk of hip fracture in three large Danish studies. They also analysed data from lactase persistence, any broken bones, and bone density from five previous studies in Northern Europe.
Drinking more milk may not protect against a broken hip
Among more than 73,000 people whose data they examined, the authors found no evidence that increasing the amount of milk we drink makes a difference to our risk of a broken hip. No marked differences were seen when milk intake was doubled from two to four glasses per week, or when milk intake was compared with no milk intake. Similarly, eating cheese wasn’t associated with any difference to hip fracture rate.
People who can’t digest lactose drink less milk…
As expected, people who couldn’t digest lactose due to ‘lactase non-persistence’ drank less milk (median of 3 glasses per week) than those who could digest lactose normally (5 glasses per week), as shown by their genetic tests.
…but are no more likely to break their hip
Despite drinking less milk, people who struggle to digest milk were not more likely to break their hip than those who could digest milk normally, the authors discovered. So being able to drink more milk does not seem to offer any protection against broken bones.
‘observationally and genetically lifelong lactase persistence was not associated with hip fracture’ – Bergholdt HKM et al, 2018.
Combining the Danish studies with the analysis of previous Northern European studies also suggested that fracture risk wasn’t affected by lactase persistence.
Bone strength was mostly similar regardless of milk intake
When it came to measuring the strength of the bones, the bone mineral densities in the hip and spine was almost the same in people who digest lactose (and therefore drink more milk) as in those who cannot digest lactose (and therefore drink less or no milk). However, milk drinkers were found to have stronger thigh bones (femoral neck density).
Can we protect ourselves from broken bones through other dairy foods, such as yogurt?
The authors point out that this study only looked at the effects of single products — milk or cheese — on the risk of broken bones. However, different types of dairy product have different characteristics. For example, in a previous study, people who increased their cheese intake were just as likely to break their hip as those that did not, whereas people who consumed different types of dairy, including yogurt, were less likely to break their hip.
It may be more relevant to look at the whole dairy matrix, and even the whole diet matrix – nutrients, fermentation and processing – which may affect how nutrients work in the body, the authors suggest.
‘the whole dairy matrix consisting of macro- and micronutrients such as fat, protein, carbohydrates, vitamins, sodium, and minerals, as well as the dairy structure … fermentation, and processing should be taken into consideration’ – Bergholdt HKM et al, 2018.
Find out more: read the original article.
Source: Bergholdt HKM, Larsen MK, Varbo A, et al. Lactase persistence, milk intake, hip fracture and bone mineral density: a study of 97 811 Danish individuals and a meta-analysis. J Intern Med. 2018 Mar 14.
