Most of us relate milk with bone health, but there is more to know about nutrients for bone health. Because we eat food and not nutrients, we will also explore foods and dietary patterns that can keep our bones healthy.
Roles of bones in the body
Bones serve a critical structural role in the body. They support all of our muscles and other tissues, allowing us to move, stand, etc. Bones also protect our internal organs (think about our ribcage) and are involved in both mineral and acid-base balance (1).
Although bones are thought to be a rigid and inert, they are actually living tissue. Bone tissue undergoes a constant process of remodelling which involves breakdown of tissue (i.e. bone resorption) by cells called osteoclasts and building of tissue (i.e. bone formation) by cells called osteoblasts.
Most of us reach the maximum bone mass in our 20s and this peak bone mass depends largely (60-80%) on genetic factors. This means that lifestyle factors can influence peak bone mass, albeit to a lesser extent than our genes (1).
Nutrients for bone health
The intake of calcium supplements early in life has been associated with greater bone mineral content, however not with a reduced risk of fractures later in life (1).
Most of the calcium in our diet comes from dairy products, followed by vegetables and fruits and other foods. The absorption of calcium depends on the source of the food (40% from dairy foods, 20-40% from vegetables such as kale and spinach) and other components present in the meal. For example, the presence of phosphopeptides, casein and whey, lactose and phosphorus enhances the absorption (or reabsorption in the case of phosphate) of calcium from dairy. On the other hand, sulphur-containing proteins and phosphate inhibit absorption of calcium from dairy, while phytic acid and oxalate inhibit its absorption from vegetables. The fact that phosphate both enhance and inhibit absorption means that we should aim for an equal or slightly higher intake of calcium than phosphate (3).
Most (~99%) of the calcium in our bodies is stored in our bones. The efficiency of this storage is regulated by life stage (i.e. growth, pregnancy and lactation) and hormones such as parathyroid hormone, calcitonin, calcitriol and oestrogen (3). The levels of this last hormone are the reason why women experience a large decline in bone mass after menopause.
Phosphate is important for the formation of bone tissue through the mineralisation of cartilage and unmineralised bone matrix. Due to the abundance of phosphate in foods, there is little need for supplementation (1).
Observational studies have led to the assumption that phosphate from animal foods is more bioavailable than from plant sources (3).
Potassium can prevent calcium loss from bones by making the body less acidic, and can also increase calcium storage in the kidneys (2).
Potassium can be found in vegetables and fruits such as green leafy vegetables, bananas and kiwifruit. The bioavailability of potassium is 60-85% (3).
Magnesium is involved in many processes that lead to improved bone health, including vitamin D activation, calcium and potassium transport, solubility of hydroxyapatite (which contains phosphorus and calcium and forms the bone matrix) and osteoblast proliferation. Low magnesium intake is associated with osteoporosis, increased calcium loss from bone and risk of fractures (2).
The absorption of magnesium is enhanced by casein, whey and potentially lactose. Magnesium from dark leafy vegetables has a low bioavailability (~25-35%) and its absorption is enhanced by protein, medium-chain triglycerides and indigestible carbohydrate. Conversely, absorption is inhibited by oxalate, phytic acid, cellulose, lignin and potentially pectin (3).
Calcium and vitamin D are found together in the bone mineral matrix (2). Both nutrients are required for bone strength (2) and work synergistically to reduce the risk of fracture (1).
More than a nutrient, vitamin D is a hormone which is mostly produced in our bodies after skin exposure to sunlight. You can learn more about vitamin D sources in my article Vitamin D and athletic performance.
Vitamin K acts as a cofactor in the process of bone matrix formation. Unfortunately, it seems that supplements are not very effective in improving bone mineral density nor risk of fractures in postmenopausal women or patients with osteoporosis (2).
There are 2 main kinds of vitamin K: K1 from plants and K2 from animal foods (e.g. fermented dairy products such as yoghurt and cheese) (3).
Vitamin C is a cofactor for osteoblast differentiation and collagen synthesis. Intake of vitamin C has been associated with increased bone mineral density and decreased risk of fracture and osteoporosis (2).
Bone mass, size and strength are associated with higher protein intake. Higher protein intakes also lead to reduced risk of fractures if calcium and vitamin D levels are adequate (1, 2).
Protein is an important component of bones (~1/3 of bone mass). Dietary protein stimulates secretion of insulin-like growth factor I (IGF-I), a hormone that is involved in the absorption of calcium and phosphorus, the synthesis of calcitriol and the reabsorption of phosphate from kidneys (2).
Protein intake paired with resistance exercise improves both muscle growth and bone strength (2).
To learn more about protein bioavailability, check out my article on protein quality and quantity.
Omega-3 fatty acids, folate, vitamin B12 and zinc may have a part to play in bone health but the relationships are not clear (2). Regardless, we should aim to meet dietary targets and address any deficiencies.
Foods for bone health
Dairy products (e.g. milk, cheese and yoghurt) contain nutrients that are important for bone health such as calcium, phosphate, magnesium and protein. In addition, some products are fortified with vitamin D (1, 2, 3).
The intake of dairy products has been associated with a greater bone mineral density (1, 2, 3). Importantly, dairy intake during pregnancy also seems to translate to higher bone mineral density of the child (1).
Although there is evidence that consumption of dairy foods early in life can lead to greater bone mineral density at an older age, this does not necessarily translate to a reduced risk of fractures (1). This could potentially be because bone mass and strength are not the only factors in the occurrence of falls and fractures.
Some studies have found no or a negative association between milk consumption and risk of fractures, depending on the population (1, 2).
Some have found that this risk is lowered with fermented dairy products such as yoghurt (1). The probiotics in fermented foods can improve vitamin D levels and calcium absorption. In addition, they may decrease the rate of bone loss associated with ageing (2).
Dietary patterns for bone health
A healthy diet as prescribed by the Australian Dietary Guidelines is associated with increased bone mineral density and decreased risk of fracture (2).
Mediterranean-style diets are associated with decreased osteoporosis and risk of fractures and higher bone mineral density. Although scientists have suggested this could be due to the higher vitamin D or intake of olive oil that are characteristic of this style of diet (2), it is likely that those are not the only factors. For example, Mediterranean-style diets are also anti-inflammatory.
Asian populations that consume high amounts of soy and fish have lower levels of fractures due to osteoporosis than Western populations. Moreover, comparisons between Asian populations show differences in bone mineral density between those consuming a less vs more processed diet (2).
Vegetarian and vegan diets
Several studies have reported that individuals who do not consume dairy products (e.g. vegans) have lower bone mineral density and higher risk of fracture than lacto-ovo-vegetarians (i.e. those who eat dairy products and eggs) and omnivores (1, 2).
- Rizzoli R. Dairy products and bone health. Aging Clin Exp Res. 2022 Jan;34(1):9–24.
- Muñoz-Garach A, García-Fontana B, Muñoz-Torres M. Nutrients and Dietary Patterns Related to Osteoporosis. Nutrients. 2020 Jul;12(7).
- Melse-Boonstra A. Bioavailability of Micronutrients From Nutrient-Dense Whole Foods: Zooming in on Dairy, Vegetables, and Fruits. Front Nutr. 2020;7:101.
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