Increasing Prevalence, Changes in Diagnostic Criteria, and Nutritional Risk Factors for Autism Spectrum Disorders

The frequency of autism spectrum disorders (ASD) diagnoses has been increasing for decades, but researchers cannot agree on whether the trend is a result of increased awareness, improved detection, expanding definition, or an actual increase in incidence or a combination of these factors. Though both genetic and multiple environmental risk factors have been studied extensively, many potentially modifiable risk factors including nutritional and immune function related risk factors such as vitamin D, folic acid, and metabolic syndrome have not received sufficient attention. Several recent studies have put forward hypotheses to explain the mechanism of association between both folic acid and vitamin D and autism. A continuous rise in the prevalence of autism in the USA has coincided with a significant enhancement of maternal folate status with FDA mandated folic acid fortification of certain foods starting in 1998. There is also a growing body of research that suggests that vitamin D status either in utero or early in life may be a risk for autism. In this communication, controversies regarding increase in estimate of prevalence, implications of changes in definition, and possible association between some modifiable nutritional risk factors such as folic acid and vitamin D and ASD will be discussed. 1. Introduction Autism, also referred to as autistic spectrum disorder (ASD) and pervasive developmental disorder (PDD), is a frequent and debilitating neurological handicap in children, which is usually diagnosed in early childhood [1]. Since there are no definitive biological markers of autism for a majority of cases, diagnosis depends on a range of behavioral signs. The major symptoms of autism involve problems with communication, social interaction, and repetitive behaviors. Because people with autism can have very different features and symptoms, autism is thought of as a spectrum disorder [2]. The complex nature of these overlapping disorders and changes in clinical definitions over time has resulted in uncertainty in monitoring the prevalence of ASD [2]. Though it is established that autism is a multifactorial condition involving both genetic and a wide range of environmental risk factors, many recently emerging factors such as de novo gene mutation and potentially modifiable nutritional risk factors have not been studied extensively [3–5]. 2. The Puzzle of Increasing Prevalence Estimates of the prevalence of the disorder in the USA and other countries are controversial and have been moving towards an apparent increase in rates. Prevalence estimates