In a study on the prevalence of multiple sclerosis in Nordland county, Norway, by Alstadhaug et al in Tidsskriftet no. 4/2005 (1), a high-risk focus was found, as in the early 1950s (2), in the area inland of Bodø. I want to mention a relevant aspect from a detailed field study by Riddervold on food and its preservation in 1900 – 40 in the nearby area of Skjerstad (3).
In comparison with eastern and central Norway, and less so with western Norway, pork consumption (by household) was definitely lower in northern Norway, still in 1977 – 79 (4). In the paper by Riddervold (3), however, a fairly high consumption of pork in the area of Skjerstad was reported, even in the coastal parts. However, even within that area, a clear gradient was apparent from the inland to coastal parts, both for the use of animal products (excluding fish, but including pork) and the intensity of smoking for preservation: it was used in ham only and for only short time (i.e. several hours) in the coastal area, but for several days and in more meat varieties (including beef and mutton) in the inland parts (3). This inland-to-coast gradient for meat smoking is in line with the overall incidence of multiple sclerosis in Norway (2). It is also in agreement with case-control studies (5, 6) linking smoking and curing with nitrate/nitrite of meat to multiple sclerosis. Nitrotyrosine is formed during inflammatory diseases of the central nervous system, including multiple sclerosis, as a consequence of peroxynitrite formation. Different nitrophenol compounds, on the other hand, are present in the meat following curing with nitrite and smoking (7), and a molecular mimicry seems therefore possible.