<unk>  can be common in people who obtain most of their food energy from corn, notably rural South America, where maize is a staple food. If maize is not nixtamalized, it is a poor source of tryptophan, as well as niacin. Nixtamalization corrects the niacin deficiency, and is a common practice in Native American cultures that grow corn, but most especially in Mexico and the countries of Central America. Following the corn cycle, the symptoms usually appear during spring, increase in the summer due to greater sun exposure, and return the following spring. Indeed,<unk>  was once endemic in the poorer states of the U.S. South, such as Mississippi and Alabama, where its cyclical appearance in the spring after meat-heavy winter diets led to it being known as "spring sickness" (particularly when it appeared among more vulnerable children), as well as among the residents of jails and orphanages as studied by Dr. Joseph Goldberger.<unk>  is common in Africa, Indonesia, and China. In affluent societies, a majority of patients with clinical<unk>  are poor, homeless, alcohol-dependent, or psychiatric patients who refuse food.<unk>  was common among prisoners of Soviet labor camps (the Gulags). In addition,<unk> , as a micronutrient deficiency disease, frequently affects populations of refugees and other displaced people due to their unique, long-term residential circumstances and dependence on food aid. Refugees typically rely on limited sources of niacin provided to them, often peanuts (which, in Africa, may be supplied in place of local groundnut staples, such as the Bambara or Hausa groundnut); the instability in the nutritional content and distribution of food aid can be the cause of<unk>  in displaced populations. In the 2000s, there were outbreaks in countries such as Angola, Zimbabwe and Nepal. In Angola specifically, recent reports show a similar incidence of<unk>  since 2002, with clinical<unk>  in 0.3% of women and 0.2% of children and niacin deficiency in 29.4% of women and 6% of children related to high untreated corn consumption. In other countries such as the Netherlands and Denmark, even with sufficient intake of niacin, cases have been reported. In this case, deficiency might happen not just because of poverty or malnutrition but secondary to alcoholism, drug interaction (psychotropic, cytostatic, tuberculostatic or analgesics), HIV, vitamin B2 and B6 deficiency, or malabsorption syndromes such as Hartnup disease and carcinoid tumors.
Pellagra
Pemphigus
Koilonychia
Kwashiorkor
Melanonychia
Porphyria
Crepitus
Photodermatitis