The adult human skeleton is made up of over 200 bones. The bones of the skeleton serve to protect vital organs and allow us to be upright and mobile. Bones are also the site at which red and white blood cells are made, as well as where essential electrolytes (such as sodium and potassium) are stored.
Bones are living tissues and as such, are in a continuous state of remodelling. There are specialised cells within bones that remove damaged tissue and other specialised cells that build new bone tissue. Bones remain strong because, throughout most of our healthy adult lives, the rate of bone breakdown is approximately matched by the rate at which new bone is built.
Both genetics and nutrition impact the structure and function of bones. For example, over 60% of a person's height is determined by genetics (Lai, 2017). The remaining determinant of height is nutrition. Particularly in childhood, protein, calcium and vitamins, A and D intake have a significant impact on height because of their necessity in bone growth, development, structure and function. Nutritional deficiencies, particularly of vitamin D and calcium, can delay or stunt growth, cause deformities in the bones as they develop, and may cause skeletal pain.
Rickets is a bone condition associated with vitamin D deficiency that can occur in children as bones are growing. Rickets causes the bones to be weak and soft, leading to deformities such as bowed legs, “knock knees,” and/or unusually thick wrists and ankles.
The development of rickets can start as early as the later part of pregnancy. The later part of pregnancy is when a baby's bones solidify – a process which requires vitamin D. A foetus gets its vitamin D from its mother, via the placenta. If the mother has low levels of vitamin D, the fetus will not get adequate amounts, and bone development may be adversely affected, leading to fetal rickets.
Whether or not a baby had exposure to adequate amounts of vitamin D in utero, adequate vitamin D intake is necessary in order to sustain normal bone growth and development once the child is born. Breast milk contains some vitamin D, likely adequate amounts for a baby from birth to six months of age. After six months, a breastfed baby would need vitamin D supplementation unless solid foods are introduced into his or her diet. Some recommend vitamin D supplementation for breastfeeding women, in order to increase the amount of vitamin D passed to the baby in breast milk. Most infant formulas are vitamin D fortified. Concern for vitamin D deficiency and rickets continues throughout childhood.
Once the bones have finished growing, in late adolescence or adulthood, rickets, which is a condition of growing bones, ceases to be a concern. A lack of vitamin D in adulthood, however, may manifest as osteomalacia, or a lack of growth of the matrix of the bone (the internal frame of the bone that enhances bone strength).
Symptoms of osteomalacia may include bone tenderness and dull, achy pain, spontaneous fractures that might not be evident until an x-ray is done, difficulty walking, and muscle weakness. Activities, even those required for daily living, may be limited by pain. In the most severe cases of osteomalacia, bone deformities can occur.
The treatment for both osteomalacia and rickets is to address the underlying cause. Sometimes treatment requires only vitamin D or calcium, in therapeutic amounts, which are considerably higher than the daily amounts recommended for maintenance.
The human body can not spontaneously make vitamin D, though it is required in order for calcium to be effective in making bone. Very little of the vitamin D we get is absorbed from the food we eat (most predominantly in vitamin D fortified dairy products and cereals). The only real food sources of vitamin D are found in fatty fish liver and egg yolks. Most vitamin D is made in our skin with sufficient exposure to ultraviolet radiation from the sun. It is a fascinating and efficient process, so long as a person gets adequate sun exposure.
Ultraviolet light exposure, however, is also implicated with increasing rates of skin cancer, as well as cosmetic skin changes such as discoloration and wrinkles. With growing concerns about skin cancer, there is an overall avoidance of the sun in much of the developed world. We have been advised to avoid being outdoors during the times the sun is the strongest, to wear hats and clothes that cover and protect our skin from the sun, and to use sunscreen or sunblock to block the ultraviolet rays from reaching the skin.
As a consequence of protecting ourselves from the skin cancer producing ultraviolet rays of the sun, we necessarily make less vitamin D. Since dietary sources of vitamin D are limited, there is growing concern for disease conditions that are caused by not having enough vitamin D. Vitamin D deficient conditions occur in bone and can manifest as rickets and osteomalacia - both are conditions that lead to weakened bones.
Vitamin D deficiency is the most common cause of rickets and osteomalacia. Rickets and osteomalacia can also be caused by low calcium levels, low phosphate levels and some medications (for example, barbiturates, phenytoin, and rifampin). Certain hereditary conditions, liver and kidney diseases, and conditions associated with poor absorption of vitamin D (celiac disease and a having had bariatric surgery, for example) may also increase the risk of developing rickets and osteomalacia.
For reference, vitamin D and calcium recommendations are as follows, and can be achieved with diet alone, or with supplementation as necessary (Misra, 2016):
- Infants: 400IU daily 200mg/day
- Children ages 1-18: 600IU daily 700-1300mg/day, depending on age
- Adults: 600IU daily 1000mg/day
- Pregnant and lactating women: 600IU daily 1300mg/day
- Menopausal women (age 50+): 600IU daily 1200mg/day
- Adults over 70 years old: 800IU daily 1200mg/day
Ideally, bone conditions associated with malnutrition, like rickets and osteomalacia, would be prevented with appropriate diet and/or supplementation.
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- Bringhurst, F. R., et al. (2014). Bone and Mineral Metabolism in Health and Disease. In Harrison's Principles of Internal Medicine (19th ed.). Eds. Dennis Kasper, et al. New York, NY: McGraw-Hill. Retrieved April 12, 2017, from http://accessmedicine.mhmedical.com/content.aspx?sectionid=79753494&bookid=1130.
- Carpenter, T. (2016). Overview of rickets in children. Uptodate.com. N.p. 2016. Web. 13 April 2017.
- Drenzer, M., (2016). Clinical manifestations, diagnosis, and treatment of osteomalacia. Uptodate.com N.P. 2016. Web. 13 April 2017.
- Lai, C.Q. (2017). How much of human height is genetic and how much is due to nutrition? Scientific American. https://www.scientificamerican.com/article/how-much-of-human-height/. 13 April 2017.
- Misra, M, (2016). Vitamin D insufficiency and deficiency in children and adolescents. Uptodate.com. N.p. 2016. Web. 13 April 2017.
- Pazirandeh, S., & Burns, D. (2016). Overview of vitamin D., In Uptodate accessed April 13, 2017.