**1.3.2 Intestinal parasites**

340 Type 1 Diabetes – Complications, Pathogenesis, and Alternative Treatments

A Norwegian study shows that children receive from 9% to 24% of their energy from added sugar in the diet, where a major part comes from soft drinks (Øverby et al., 2004). Despite the fact that the increase in intake of simple sugar (in the form of sweets and drinks) in ecological studies correlate with increasing incidence of T1D, only a couple of studies have attempted to investigate this at the individual level. In one study an association between sugar intake and T1D incidence was not found (Dahlquist et al., 1990), but in two more recent studies a correlation was found (Pundziute-Lycka et al., 2004; Benson et al., 2008). Both studies used a case-control design which is likely to suffer from recall bias. Prospective studies with proper registration of dietary habits are therefore needed. The role of diet at

A few studies have observed an association between high birth weight and increased risk of T1D (Stene et al., 2001), although the relation is not very strong, but overweight and obesity are increasing. Gestational diabetes in the mother is a risk factor for a high birth weight and gestational diabetes has increased the last decades. Today a considerable proportion of pregnant women have gestational diabetes. Gestational diabetes may be a consequence of increased body weight in connection with the increased insulin resistance following pregnancies in general. Data from the MIDIA study indicate that both the mothers Body Mass Index (BMI) before getting pregnant as well as high weight gain during pregnancy increase the risk for autoimmunity at an early age for the offspring (Rasmussen et al., 2009). Obesity during childhood is emerging as a possible risk factor for T1D (EURODIAB, 2002; Pundziute-Lycka et al., 2004), but further studies are needed, including to find what particular aspects of body size/obesity (such as inflammatory cytokines or other markers) are most relevant in this relation. Since all the potential relations described above have very important public health implications, the different factors need to be investigated in larger

The hygiene hypothesis states that the lack of exposure to parasites, symbiotic organisms and infectious agents in early childhood increases the susceptibility to allergic and autoimmune diseases (Zazdanbakhsh et al., 2001). Since humans have evolved coexisting in a shared environment with microbial agents throughout much of our evolutionary history, these agents might be necessary for the development of a balanced and regulated immune system (Stoll, 1947). The decline in non-specific infectious and microbial exposure in many populations is thus proposed to be the cause of the concomitant increase in atopic disorder over the past few decades (Bachlin & Degremont, 1997), and this hypothesis has been

The hygiene hypothesis is supported by epidemiological studies that show higher prevalence of autoimmune diseases in North America and Europe compared to South America and Africa, higher incidence associated with increased material wealth and higher risk for autoimmune diseases for third world immigrants to the industrialized countries (Herrström et al., 2001). There are also many studies showing that some infections and microbial agents reduce the incidence of autoimmune diabetes in experimental animals

extended to autoimmune diseases such as T1D (Kyronseppa, 1993).

**1.3.1 The hygiene hypothesis and epidemiology** 

different ages in a child's life may also be important.

**1.2.6 Sugar** 

**1.2.7 Overweight** 

well-designed prospective studies.

**1.3 The hygiene hypothesis** 

Since immunomodulatory effects of parasites have been reported (Samulsson & Ludvigsson, 2003), and there is evidence that infections protect against the development of allergic disorders, parasites become obvious and major candidates for the hygiene hypothesis. In 1947 it was reported that 40-60% of European children were positive for helminths (Horman et al., 2004), while in recent years only 5-23% are found positive (Strachan, 1989; Jones et al., 2000; Yazdanbakhsh et al., 2002; Cooke, 2009; Bach, 2002; Honeyman, 2005; van der Werf et al., 2007; Gibbon et al., 1997; Parslow et al., 2001; Pundziute-Lycka et al., 2003; Round & Mazmanian, 2009). The most prevalent of the helminths is Enterobius Vermicularis (pinworm) which is usually asymptomatic and each bout is self-limiting since the worms cannot reproduce within the gut. Most common of the water borne parasites are Cryptosporium and Giardia. While the genus Giardia comprises six species, more than 20 variants of Cryptosporium are known (Nygard et al., 2003).
