Discussion

The results of the present study indicated that the proportion of children with vitamin D deficiency in ADHD group was significantly larger than that of the normal children. In addition, the mean value of serum vitamin D level in the cases group (19.11±10.10) was significantly lower than in the control (healthy) group (28.67±13.76). This finding is consistent with the report of a similar study conducted in Turkey among 7 to 18 years old children where a significant difference (P < 0.05) in mean serum vitamin D level between cases (20.9±19.4 ng/ml) and control groups (34.9±15.4 ng/ ml) was demonstrated (28). Another study on 1331 cases of ADHD and the same number of control groups healthy individuals under the age of 18 found out that the mean range serum vitamin D level of ADHD children (16.6±7.8 ng/ml) was lower than in the control group (23.5±9.9 ng/ml). In addition, 8.15% of the ADHDs had normal vitamin levels in their serum (29). These results are also similar to what was found in our study as previously stated. In an interventional study on 80 patients with ADHD above the age of 16 in New Zealand, reported 27% prevalence rate of vitamin D deficiency. Using vitamin D supplement for eight weeks was found to be effective in alleviating the signs of the disease. However, adding other micronutrients such as zinc, vitamin B12, iron and folate was not found effective (30). In contrast, another study in England reported no significant association between some behavioral problems including ADHD and vitamin D level (31). The incidence of ADHD is much lower in areas with sunny weather and sunlight can have a protective effect against the disease (32). Phototherapy and sunray have been used as a treatment (33, 34). A hypothesis in this regard is that sunrays increase the level of vitamin D level (32). Several studies have been conducted to identify the role of nutrition on the prevalence of the disease, however, many of them have emphasized on the role of breast feeding. These studies assume that the nutrient contents of breast milk such as vitamins, minerals, etc. may act as protective agents. However, there is a need for further investigations (35-38). Various studies have examined the effects of micronutrients such as iron, zinc and omega 3 on ADHD, but there is limited evidence suggesting the association between vitamin D deficiency and ADHD. Thus, further studies seem necessary (14-19, 39). Although little research has implicated the relationship between ADHD and vitamin D, extensive studies have investigated the role of this vitamin in other psychiatric/ neurologic disorders (40, 41) including Alzheimer’s disease (42) depression (43, 44), schizophrenia (45) and autism (46). Since vitamin D is a neurosteroid, lack of this vitamin results in many psychological disorders (20). In addition, vitamin D plays a protective role in brain health, that is, it increases the expression of transpeptidasec-glutamyl. This enzyme enhances the formation of glutathione, which is the most important brain antioxidant factor (47). Lack of this vitamin during the fetal life and childhood, in the very early days of life affect the nerve differentiation, axon synapses, brain structure, and function (20). In the present research, although a considerably high percentage of children in the ADHD had vitamin D deficiency, healthy children in the control was also found to have suffered from vitamin D deficiency. Vitamin D deficiency is a worldwide epidemic. Despite the abundance of sunlight, the prevalence of vitamin D deficiency in countries located around the Persian Gulf region is high. Findings indicated that 70% of very young girls in Iran and 80% in Saudi Arabia suffered from vitamin D deficiency (48). Exposure to sunlight alone is not sufficient to alleviate vitamin D deficiency despite sun light plays a role in maintaining vitamin D level in blood (49).

In conclusion, the low levels of serum vitamin D among the ADHD children suggest the need for regularly monitoring of serum vitamin D levels and treatment of patients with vitamin D deficiencies. In addition, life style and diet should be modified and directed towards eliminating the nutritional deficiencies in the society.