Rickets is a disease of the hypertrophic chondrocytes in the skeletal growth plate resulting in a softening of bones in children. Rickets is characterized by impeded growth and deformity of the long bones.
Osteomalacia is the milder, adult form of the disease. Osteomalacia symptoms include diffuse body pains, muscle weakness, and fragility of the bones. In osteomalacia, 25-D levels are very low, and 1,25-D is undetectable.
Lack of vitamin D is erroneously believed to be a cause of rickets and osteomalacia. However, low levels of vitamin D are merely associated with the disease. This study concluded, "Increased habitual calcium intake lowered markers of bone turnover. Acute ingestion of a calcium load lowered PTH and bone turnover markers. Additional intake of 100 microg/d vitamin D(3) did not lower PTH or markers of bone turnover."[1]
Both rickets and osteomalacia are caused by defective bone mineralization secondary to inadequate amounts of available phosphorus and calcium.
Phosphorus plays a critical role in cartilage and bone metabolism. Hypophosphatemia (a low phosphorus level) is the common denominator and the proximate cause of all rickets. [2]
In osteomalacia, low serum phosphorus and high serum alkaline phosphatase (ALP) are characteristic. Serum calcium may be low or normal, depending on the effectiveness of secondary hyperparathyroidism in restoring serum calcium to normal. The parathyroid hormone (PTH) is elevated and urinary calcium is low in all forms of the disease except those associated with acidosis.
Calcium deficiency is the most common ultimate cause of rickets and osteomalacia in the developed world. Many people do not consume enough calcium, but it's quite difficult to eat a diet without enough phosphorus because phosphorus is abundant in foods. Low calcium intake leads to hyperparathyroidism, which leads to high phosphorus excretion and thus phosphorus deficiency.
The solution to low phosphorus is not to ingest more phosphorus. A high phosphate level is a cause of secondary hyperparathyroidism and can be a problem for those with poor kidney function.
An adequate calcium intake is the way to prevent rickets and treat osteomalacia. Calcium intake (including both food and supplements) should be maintained near the Recommended Daily Allowance. Too much calcium should be avoided because it could interfere with normal endocrine metabolism.
[1] The relative influence of calcium intake and vitamin D status on serum parathyroid hormone and bone turnover biomarkers in a double-blind, placebo-controlled parallel group, longitudinal factorial design.
Aloia J, et al
Bone Mineral Research Center, Winthrop University Hospital, Mineola, NY
J Clin Endocrinol Metab. 2010 Jul;95(7):3216-24. Epub 2010 May 12.
[2] Hypophosphatemia: the common denominator of all rickets.
Tiosano D, Hochberg Z.
Meyer Children's Hospital, Rambam Medical Center, POB 9602, 31096, Haifa, Israel.
J Bone Miner Metab. 2009;27(4):392-401. Epub 2009 Jun 6.
