Rickets was once considered an extremely common disorder of childhood. The term itself is derived from the old English word for “twist,” or “wrick,” and throughout history children with rickets could be identified by their bowed legs and knock knees, which gave them a twisted appearance.
Rickets is caused by a deficiency in vitamin D. During growth, human bone is made and maintained by the interaction of calcium, phosphorus, and vitamin D. Calcium is deposited in immature bone (osteoid) in a process called calcification, which transforms immature bone into its mature and familiar form. However, in order to absorb and use the calcium available in food, the body needs vitamin D. In rickets, the lack of this important vitamin leads to low calcium, poor calcification, and deformed bones.
Vitamin D is the only vitamin that can be both acquired through food and made by the body itself. Although vitamin D can be absorbed through foods rich in animal fat, such as milk, cheese, fish, and meat, this absorption constitutes only about 10 percent of what the body needs in a single day. The remaining 90 percent is created by the body. Ultraviolet radiation from the sun converts 7-dihydrocholesterol in the skin to vitamin D3. This is then converted to the hormone calcitriol (the active form of vitamin D) in the kidney. Calcitriol allows absorption of calcium and phosphorus in the gut, primarily in the small intestine, and maintains the body’s balance of calcium and phosphate through the kidney and bone. Without adequate vitamin D, the body can only absorb 10 to 15 percent of the calcium available in food. This balance of vitamin D, calcium, and phosphate is essential to the growth and maintenance of bones, especially in children. Deficiencies can also occur in elderly adults, a condition called osteomalacia.
Historically, rickets plagued the populations of European countries in the northern latitudes—at one time it was called “the English disease.” During the Industrial Revolution and into the early 1900s, smog filled the developing cities of Europe, diminishing the amount of sunlight to which children were exposed and causing an epidemic of rickets. Some researchers estimate that prior to 1915, almost 85 percent of children in these industrialized areas of Europe and North America suffered from rickets. With research into the sources and function of vitamin D in the 1920s, however, the use of cod-liver oil, fortified cow’s milk, and fortified formula virtually eliminated rickets in Europe and North America.
This child’s bowed legs are a symptom of rickets, a disease resulting from vitamin-D deficiency. Because their skin absorbs less sunlight, dark-skinned people need more sun exposure to synthesize the recommended daily amount of vitamin-D. This child’s bowed legs are a symptom of rickets, a disease resulting from vitamin-D deficiency. Because their skin absorbs less sunlight, dark-skinned people need more sun exposure to synthesize the recommended daily amount of vitamin-D.
As vitamin D can either be consumed in small quantities through the diet or made in the skin, there are two main groups of risk factors for developing rickets. Dietary risk factors include diets low in vitamin D–rich foods, such as eggs, cow’s milk, meat, and fish. Breast milk, a primary source of childhood nutrition, contains very little vitamin D, and infants who are exclusively breastfed are more likely to develop the disease. While human milk does contain sufficient amounts of calcium and phosphorus for an infant, its vitamin D content is only 4-60 IU/L (international units per liter), while the full-term infant requires approximately 400 IU daily. Infants and children who are not exposed to sunlight, like those in smog-filled cities or those who remain indoors or covered for cultural or religious reasons, are also at increased risk of developing rickets. In children with darkly pigmented skin, melanin acts in a similar way to block sunlight’s ability to help the skin make vitamin D. Dark-skinned people require almost six times as much sunlight exposure to make the same amount of vitamin D as those with lighter skin.
Populations that remain at risk today include people with darkly pigmented skin, those who live in industrialized northern cities, and children in certain Arab countries where covering clothing and staying indoors during early childhood are cultural norms. Even in tropical and sunny climates, rickets remains a problem in dense city centers like Calcutta and Johannesburg, and it is still diagnosed in mostly African-American children in the United States. Children who consume vegetarian or vegan diets, as well as infants of lactating mothers who have chronically low levels of vitamin D, may also be at increased risk for rickets. Although rare, diets directly deficient in calcium and/or phosphorus may also lead to rickets.
One of the earliest signs of rickets in the infant is craniotabes (a softening of the skull) and delayed closing of the anterior fontanelle (the soft spot on the head). The infant’s skull becomes large and thick (though soft), and muscle tone is poor. Poor calcification of osteoid at the ends of bones makes the bone spread in that area. At the ends of ribs, these splayed areas create a knobby-looking chain called the “rachitic rosary” on the front of the chest. In other areas, the pressure of a child’s weight bends poorly mineralized bones, creating shortness, bow legs, and knock knees. Poor calcification also creates weakness, making bones prone to fracture. Children can also have delayed dentition, pelvic abnormalities, and enlarged joints, along with a curved spine and a forward projected breastbone. Rickets also lowers a child’s immune defenses. For those with severe and untreated disease, bone bowing, short stature, and fractures can lead to long-term pain and immobility and require bracing and/or surgery.
Luckily, rickets is a very treatable and preventable disorder. Researchers have found that as little as twenty to thirty minutes of sun exposure per week in children in temperate climates is sufficient to maintain adequate levels of vitamin D in the blood. Other studies have found that oral supplements of 400 IU of vitamin D daily, often in the form of fish-liver oil, can prevent the disease in at-risk populations. Supplementation can also aid in the healing process. A single dose of 600,000 IU, or gradual treatment with 5,000–10,000 IU daily for two to three months, can be a sufficient treatment. And although some bony deformities may remain, many will repair themselves, and most growth parameters will return to near normal. Treatment can prevent grave complications, including developmental delays, waddling gait, and seizures.
Once a widespread scourge of childhood, rickets is now a preventable and treatable disease. It is necessary to understand the roles of vitamin D, calcium, and phosphorus in bone growth, as well as the mechanism of the disease in order to appropriately diagnose and treat it. When addressing the global impact of this disease, it is especially important to understand local environments, community diets, and cultural beliefs.