The most important nutrients required for growth and development of bones with children and for healthy bones all life through are calcium, vitamin D, protein, phosphorus. Besides these four nutrients, magnesium, zinc and vitamin C are needed for the maintenance of normal bones.1,2 Therefore it is important to get a sufficient amount of these nutrients as shown in table 1.3,4 The composition and structure of the bone tissue is mainly determined by calcium, phosphorus and protein.
Calcium is an important building block for the bones, including our teeth. As 99% of the calcium in the body is stored in the bones the bone tissue plays a crucial role in calcium metabolism. Calcium is absorbed both actively and passively in the intestine. The active process chiefly takes place in the first part of the small intestine and depends on calcitriol (1,25-dihydroxyvitamin D), which is obtained through a stepwise activation of vitamin D by the liver and the kidneys. Active calcium absorption also depends on vitamins D2 and D3, obtained from the food or through 7-dehydrocholesterol activation by sunlight in the skin (previtamin-D3). The passive absorption takes place by means of diffusion in virtually all parts of the small intestine and a minor part in the large intestine. The active absorption is particularly relevant in case of a low calcium intake. A low solubility of calcium in the lumen of the intestine, for example as a result of complex formation with phytate from grains or oxalate from spinach, reduces the availability for absorption. A high calcium density in food provides more available calcium through the passive transport along the intestinal wall.6 The physiological aspects, such as calcium intake in the past, age (absorption decreases when getting older), pregnancy, breastfeeding (higher calcium absorption) and the vitamin D status, are decisive for the availability of the consumed calcium.3,4
In general, foods such as milk, milk products and cheese are considered to be good sources of calcium because of their high calcium density and good fractional absorption (under normal conditions about one third of the available calcium is absorbed).8 A glass (150 ml) of semi-skimmed milk contains 183 mg calcium. Vegetables that contain calcium and are low in oxalate are broccoli, sweet potato, kale and bok choy.3 Their calcium content per serving ranges from 35 to 79 mg.8 Calcium and dairy intake recommendations differ per age category and per region in the world.3,9,10
Vitamin D is most efficiently absorbed from the intestine when fat is present. In the intestinal cells it is packaged in the chylomicrons, together with cholesterol, triglycerides and lipoproteins, and it reaches the bloodstream through the lymph system. The liver hydroxylates vitamin D into 25-hydroxyvitamin D (25OH-D) and the kidneys take care of the production of the hormone calcitriol, the biologically active vitamin D. Calcitriol stimulates the absorption of calcium and phosphate from the intestine, which is required for mineralising the bone tissue. Together with the parathyroid hormone (PTH) from the parathyroid glands (parathyroids), calcitriol also controls the release of calcium from the bone and the retention of calcium by the kidneys, depending on how much calcium the body needs. A third hormone, calcitonin produced by the thyroid reacts to too high calcium values in the blood serum by limiting the bone resorption. Vitamin D also has a direct effect on the production and differentiation of osteoclasts (bone resorption cells).3,4,5
25-hydroxyvitamin D is generally considered to be a robust and reliable parameter of the vitamin D status. An intensive discussion is going on about which threshold values are to be used for this indicator with respect to specific target groups within the population or health areas.11
Fat fish types, such as herring, salmon and mackerel, contain vitamin D are good sources which are generally imported from overseas and can be quick expensive.
Protein is a building block for strong muscles and bones. This macronutrient plays a role in the growth and preservation of the muscle mass and the maintenance of the bone mass .1,2 Dairy products, eggs, fish, meats, tofu and legumes are good sources of protein.
Protein in food increases the production of IGF-1 (Insulin-like Growth Factor) by the liver. As IGF-1 stimulates the calcitriol production in the kidneys, the systemic availability of calcium and phosphorus increases as well (Bonjour et al., 2013). A higher protein intake may lead to a higher acidity of the blood and so a higher calcium level in the urine (Fenton et al., 2008). It was demonstrated that this does not have any effect on the calcium balance in the body, which is the difference between the calcium intake through food and the excretion through urine and faeces. In case of a higher protein intake, the body actually also absorbs more calcium from food.12,13
A low protein intake is associated with a decrease of the muscle mass. With elderly people a too low protein intake is associated with muscle weakness and sarcopenia, which raises the risk of falling.3,4
Phosphorus makes a contribution to the maintenance of the bone mass.1 Phosphorus is particularly found in dairy products, wholemeal products, cheese, meat, fish and legumes. 85% of the total amount of phosphorus present in the body is stored in the bones.
Inorganic phosphate passes the intestine through both active and passive transport. The serum values for phosphate are largely determined by the consumed amount, calcitriol (absorption from intestine and bone) and PTH (resorption from bone, increase of excretion by kidneys). Apart from this osteocytes in the bone tissue produce the hormone FGF-23 (fibroblast growth factor 23). FGF-23 decreases the absorption of phosphate from the intestine and increases the excretion by the kidneys. The osteocytes are involved in the mineralisation process in the bone and seem to play a regulating role in the functioning of both osteoblasts (formation) and osteoclasts (resorption).14
The phosphorus requirement is closely related to the calcium requirement. A recent meta-analysis of calcium balance studies in relation with the intake of phosphate supplements showed that a higher phosphate intake lowers the excretion of calcium in the urine and slightly raises the calcium retention, independent of the calcium intake.15
- EFSA claims: 2009; 7(9):1210,1219, 1272.
- EFSA claims: 2010; 8(10):1725, 1811
- Milk and dairy products in human nutrition. Food and Agriculture Organization 2013. Rome.
- International Osteoporosis Foundation. Invest in your bones. How diet, life style and genetics affect bone development in young people. International Osteoporosis Foundation, 2001. Zwitserland, Nyon.
- Bonjour JP, Kraenzlin M, Levasseur R, Warren M, Whiting S et al. Dairy in adulthood: From foods to nutrient interactions on bone and skeletal muscle health. Journal of the American College of Nutrition, 2012; 32(4):251–263.
- Calcium in nutrition. ILSI Europe Concise Monograph Series. International life sciences institute, Brussel, België, 1999.
- Weaver CM, Heaney RP et al. Calcium in human health. Weaver M. en Heaney R.P., Eds. Human Press, Totawa, NJ, 2006.
- Miller GD, Jarris JK, McBean LD (eds.). Handbook of dairy foods and nutrition, 3rd edition, CRC Press, NY, 2007.
- Dror DK and Allen LH. Dairy product intake in children and adolescents in developed countries: trends, nutritional contribution, and a review of association with health outcomes. Nutrition Reviews 2013; 72(2):68-81.
- Dietary Reference Intakes for Calcium and Vitamin D. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium Washington (DC): National Academies Press (US); 2011. http://www.ncbi.nlm.nih.gov/books/NBK56061
- Cashman, K.D. en Kiely, M. EURRECA—Estimating Vitamin D Requirements for Deriving Dietary Reference Values, Critical Reviews in Food Science and Nutrition, 2013; 53:10, 1097-1109, DOI:10.1080/1040839 8.2012.742862.
- Calvez, J., Poupin, N., Chesneau, C., Lassale, C. en Tomé, D. Protein intake, calcium balance and health consequences. European Journal of Clinical Nutrition, 2012; 66(3):281-295.
- Kerstetter, J.E., Kenny, A.M. en Insogna, K.L. Dietary protein and skeletal health: a review of recent human research. Current opinion in lipidology, 2011; 1:16-20.
- Penido, M.G.M.G. en Alon, U.S. Phosphate homeostasis and its role in bone health. Pediatric Nephrology, 2012; 27(11):2039-2048.
- Fenton, T.R., Tough, S.C., Lyon, A.W., Eliasziw, M. en Hanley, D.A. Causal assessment of dietary acid load and bone disease: a systematic review & meta-analysis applying Hill’s epidemiologic criteria for causality. Nutrition Journal 2011; 10(41).