It can be tempting to think of our bones as inert; a scaffold like a steel framework that holds our living tissues together. However, bones are dynamic organs that are continuously being remodelled in response to the environment that they find themselves in. In simplified terms, there is a balance between cells that build new bone (called osteoblasts) and cells that break down old bone (osteoclasts).
A cancer diagnosis often has an impact on bone health due to the altered environment in the body. Treatment can plunge many women into menopause, and the drop in oestrogen favours the production of osteoclasts, which leads to reductions in bone mineral density. Add aromatase inhibitors (such as letrozole, anastrozole or exemestane) into the picture, and there is further risk of reduced bone mineral density(1). After a cancer diagnosis, all of us should be taking measures to look after our bones!
Exercise
Good news for all members of Get Me Back: exercise acts as information for bones. As important as nutrition is, exercise is more critical for maintaining healthy bones. When tendons or ligaments pull on bones, the mechanical stress tells bones that they need to be strong. Exercise also improves balance, so that falls and resultant fractures are less likely(2).
Calcium
Calcium is the most abundant mineral in the human body, and most of that calcium is found in our bones and teeth.
One common misconception is that if your serum calcium level is in normal range on a blood test, you are getting enough calcium from your diet and you have enough in your bones. Unfortunately, it is not possible to tell this from a serum calcium test. Blood concentrations of calcium are critical for many bodily functions, including regulating heart muscle function, facilitating nerve signalling and affecting the stability of the membranes around all body cells. Because calcium has such important roles, the body works hard to keep serum levels within a tight range. Serum calcium only tends to go out of range if there is an underlying medical condition which affects this careful balance.
Milk and dairy products are the most concentrated food sources of calcium. However, there are many other foods that also contain significant amounts of calcium, and often in a more bioavailable form. Calcium from cruciferous vegetables (such as kale or broccoli) is absorbed twice as efficiently as calcium from dairy. Small bones eaten with tinned sardines or salmon are a valuable source. Dark green leafy and cruciferous vegetables, soy products such as tofu, almonds and sesame seeds all contain significant amounts of calcium.
It is best to obtain as much of the calcium you need as possible from the diet. Excessive calcium supplementation can promote an insufficiency of magnesium (as we will soon discuss). However, follow your doctor’s advice if you have been prescribed calcium supplements.
Here is a list of the calcium content in some dairy and non-dairy foods, but remember that this does not address differences in intestinal absorption.
Food Calcium content, mg
100ml whole cows’ milk 124
100g whole milk natural yoghurt 132
25g feta cheese 123
100g sardines with bones 382
100g extra firm tofu 375 (although may be as much as 680mg,
depending on the preparation method)
240g chickpeas 77
30g almonds 70
100g kale 72
1 tbsp tahini paste 64
100g broccoli (approx. ½ head) 40
100g broad beans 36
Vitamin D
Vitamin D is another key nutrient for bone health. Adequate vitamin D increases the amount of calcium and phosphorous that can be absorbed from food in the gut. Without enough vitamin D, only 10-15% of dietary calcium is absorbed; this increases to 30-40% in the presence of sufficient vitamin D(3).
Restoring vitamin D levels to adequate amounts also has also been shown to reduce the risk of falls in the elderly(4). Some research suggests that serum levels of 25(OH) vitamin D of at least 50 nmol/L are sufficient for optimum bone health, while other sources recommend 75 – 80 nmol/L as optimal levels.
Vitamin K
Vitamin K is a fat-soluble vitamin. Vitamin K’s relevance to bone health is that it activates a protein called osteocalcin, which binds calcium into bone. In other words, vitamin K helps ensure that dietary calcium finds its way into the skeleton, where we want it to be.
The most concentrated dietary sources of vitamin K are green leafy vegetables, such as kale, spinach and broccoli. Supplementation of vitamin K along with vitamin D and calcium has been found to increase bone mineral density in healthy postmenopausal women(5).
Magnesium
Although it is often overlooked, magnesium is as important for bone health as calcium. There are several reasons for this. Magnesium is needed to convert vitamin D into its active form. It stimulates the activity of the bone-building osteoblasts, and affects parathyroid hormone, which is involved in regulating calcium levels. A magnesium deficiency can promote inflammation, which results in higher activity of osteoclasts(6).
Calcium and magnesium compete with each other for absorption, so excessive consumption of one can lead to an insufficiency of the other. Some of the best dietary sources of magnesium are dark green leafy vegetables, legumes, nuts and seeds, wholegrains and tofu. Note that many of these are also good sources of calcium!
Nutritional factors which adversely affect bone health
A high caffeine intake (more than 2 cups of coffee per day) reduces calcium absorption in the gut
A diet high in salt can increase the rate of urinary calcium excretion
Dark soft drinks (mainly colas) contain phosphoric acid, which have an adverse impact on the bones(7), (8).
Inflammation promotes osteoclast activity which leads to reduced bone mineral density(9) – another great reason to adopt an anti-inflammatory diet!
Finally, a low body mass index is consistently associated with an increased risk of fractures(10). In terms of bone health, it is better not to be at the lower end of the healthy body mass index range.
References
1. Tenti, S., Correale, P., Cheleschi, S. et al. (2020). “Aromatase Inhibitors—Induced Musculoskeletal Disorders: Current Knowledge on Clinical and Molecular Aspects”, International Journal of Molecular Sciences, 21(16), 5625. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7460580/ (Accessed 4 July 2023).
2. Chang, X., Xu, S. and Zhang, H. (2022). “Regulation of bone health through physical exercise: Mechanisms and types”, Frontiers in Endocrinology, 13: 1029475. Available at https://www.frontiersin.org/articles/10.3389/fendo.2022.1029475/full#h6 (Accessed 4 July 2023).
3. Khazai, N., Judd, S.E. and Tangpricha, V. (2008). “Calcium and Vitamin D: Skeletal and Extraskeletal Health”, Current Rheumatology Reports, 10(2), pp110-117. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2669834/ (Accessed 4 July 2023).
4. Ling, Y., Xu, F., Xia, X. et al. (2021). “Vitamin D supplementation reduces the risk of fall in the vitamin D deficient elderly: An updated meta-analysis”, Clinical Nutrition, 40(11), pp5531-5537. Available at https://pubmed.ncbi.nlm.nih.gov/34656949/ (Accessed 4 July 2023).
5. Bolton-Smith, C., McMurdo, M.E.T., Paterson, C.R. et al. (2009). “Two-Year Randomized Controlled Trial of Vitamin K1 (Phylloquinone) and Vitamin D3 Plus Calcium on the Bone Health of Older Women”, Journal of Bone and Mineral Research, 22(4), pp509-519. Available at https://asbmr.onlinelibrary.wiley.com/doi/full/10.1359/jbmr.070116 (Accessed 5 July 2023).
6. Ciosek, Z., Kot, K., Kosik-Bogacka, D. et al. (2021). “The Effects of Calcium, Magnesium, Phosphorus, Fluoride, and Lead on Bone Tissue”, Biomolecules, 11(4), 506. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8066206/ (Accessed 5 July 2023).
7. Tucker, K.L. (2009). “Osteoporosis prevention and nutrition”, Current Osteoporosis Reports, 7(4), pp111-117. Available at https://pubmed.ncbi.nlm.nih.gov/19968914/ (Accessed 6 July 2023).
8. Høstmark, A.T., Søgaard, A.J., Alvær, K. et al. (2011). “The Oslo Health Study: A Dietary Index Estimating Frequent Intake of Soft Drinks and Rare Intake of Fruit and Vegetables Is Negatively Associated with Bone Mineral Density”, Journal of Osteoporosis, 2011:102686. Available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3135045/ (Accessed 6 July 2023).
9. Livshits, G. and Kalinkivich, A. (2022). “Targeting chronic inflammation as a potential adjuvant therapy for osteoporosis”, Life Sciences, 306:120847. Available at https://pubmed.ncbi.nlm.nih.gov/35908619/ (Accessed 6 July 2023).
10. Stránský, M. and Ryšavá, L. (2009). “Nutrition as prevention and treatment of osteoporosis”, Physiological Research, 58 Suppl 1, S7-S11. Available at http://www.biomed.cas.cz/physiolres/pdf/58%20Suppl%201/58_S7.pdf (Accessed 6 July 2023).