What are the causes for Diffuse Idiopathic Skeletal Hyperostosis (DISH)?

The exact cause of DISH is not known. A variety of factors are thought to contribute to its development, such as metabolic conditions. For example, DISH is more common in obese people and those with diabetes, as well as up to 20% of people with acromegaly (a rare condition caused by abnormal levels of growth hormone). It is more common in men than women and the elderly. DISH is uncommon before age 40.

Source: http://www.emedicinehealth.com