A study of plasma levels of zinc in children with pica in a public hospital setup

Background: Pica is the craving and purposeful consumption of non-food substances. In children with pica, there is a greater possibility of zinc deficiency. Objectives: To study the plasma levels of zinc in children having pica and to study the efficacy of pica as a clinical marker of zinc deficiency. Method: This is a case control study of children attending the outpatient department of a tertiary health centre. A total of 92 children were enrolled in the study, of which 46 children who had the habit of pica were taken as cases and the remaining 46 children without the habit of pica were enrolled as controls. Serum zinc levels of the 92 children were estimated. Results: Of the 92 children included in the study, 56% of cases and 47% of controls belonged to the age group of 2 to 2.5 years. It was observed that 96% of cases had zinc deficiency whereas 100% of controls had normal zinc levels. The mean zinc level of the cases was 46.73±21.32mcg/dL compared to 148.5±15.4mcg/dL in the controls. Accuracy of pica as a clinical marker of zinc deficiency was 97%. Conclusions: The mean zinc level of the cases who had pica was significantly lower than the mean zinc level of the controls indicating that pica is a useful clinical marker for zinc deficiency.


Introduction
Pica is the craving and purposeful consumption of non-edible substances; it includes geophagy (consumption of earth), amylophagia (consumption of raw starch), pagophagia (consumption of ice) and other forms of non-food consumption and is more prominent in younger children 1,2 . Adverse effects of pica range from parasitic infestation 3 , anaemia 4 , trichobezoar and intestinal obstruction 5 , to life-threatening hypokalaemia 6 and lead poisoning 7,8 . Aetiology of pica is still controversial. Specific prevalence rate for children is unknown 9 . It is estimated that pica occurs in 75% of 12-monthold infants and 15% of 2-3-year-old children 10 . Micronutrients are nutrients required by organisms throughout life in small quantities to organize a range of physiological functions 11 . Pica is sometimes found in conjunction with micronutrient deficiencies and the direction of this relationship is not well understood 12 . There are two mechanisms by which pica may cause these deficiencies. Pica material may bind to the mucosal layer of the gut, thereby preventing absorption of micronutrients; this material may also absorb micronutrients in ingested food, preventing them from being metabolized. Conversely, it has been suggested that micronutrient deficiencies cause humans to seek out minerals from non-edible substances 13 . The micro minerals or trace elements include iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc, and molybdenum 2 . Micronutrients also include vitamins which are organic compounds required as nutrients in trace amounts 14 .
Zinc acts as an antioxidant to protect the body against free radical damage 15 . It is an essential component of several enzymes e.g., carbonic anhydrase, alcohol dehydrogenase, etc. and is necessary to maintain the normal levels of certain vitamins and hormones 15 . It is required for wound healing 15 . Zinc enhances cell growth and division, besides stabilizing bio membranes and also protects against infections 15 . Zinc deficiency is associated with growth retardation, poor wound healing, anaemia, loss of appetite, loss of taste sensation and neuropsychiatric disorders like depression, dementia etc. 15 . Prevalence of zinc deficiency in children aged 6 to 60 months in India is 43.8% 16,17 . In children having pica there is the possibility of more severe zinc deficiency.

Objectives
 To study the plasma levels of zinc in children having pica  To study the usefulness of pica as a clinical marker of zinc deficiency.

Method
This was a one-time observational case-control study conducted over a period of one year in the Department of Paediatrics of a tertiary healthcare centre. Forty-six children who fulfilled the definition of pica as per DSM-5 criteria (age >2 years and duration of ingestion for at least 1 month) were randomly selected as a study group. We also studied zinc levels in a control group (46 children without the habit of pica) coming to the paediatric outpatient department (OPD). Sample size was determined by using statistical tool OpenEpi version 2.2 Inclusion criteria: Children enrolled on an OPD basis having pica according to DSM-5 criteria were included in the study as cases and children enrolled on an OPD basis without pica were included as controls matched for age, sex, socio-economic status and anthropometry with cases of the study group.
Exclusion criteria: Children who were very sick, with developmental delay, with chronic illness or with moderate /severe malnutrition (according to IAP classification) were excluded from the study. The detailed proforma was filled after taking a detailed history regarding the habit of pica as to what type of non-food items patient was eating, age of onset of ingestion of non-food items, frequency of ingestion of non-food items, any similar history in the past, family history, siblings having the similar history of pica, along with a thorough clinical examination to rule out any significant problems fitting into the exclusion criteria. Detailed anthropometry was done in all cases and controls enrolled in the study according to inclusion criteria. Age of study population was taken as per the date of birth mentioned by their parents. Blood (3 mL) was collected from a peripheral vein into trace element-free, heparinized plastic vials using disposable plastic hub bed needles. Plasma zinc levels were determined with the help of thermos-scientific I.C.E. 3000 series aa spectrometer. The reference range of zinc according to this method is 80-120µg/dL. In our study all subjects with zinc levels <80µg/dL were taken as zinc deficient and further sub-classified as mildly (60-80µg/dL), moderately (31-59µg/dL), and severely (<30µg/dL) deficient.  Table 1 shows the age distribution of cases with pica and controls. It was found that the cases and controls are well matched for age. (p> 0.05) 29.87 ± 9.06 32.21 ± 11.83 0.289 Figure 1 shows 45% males and 54% females among cases and 63% males and 36% females among controls. It was found that the cases and controls are well matched for gender with a p value of 0.09. Table 2 shows the comparison of the nutritional status of the study population and the mean zinc levels. Figure 2 shows the types of non-food substances ingested by the cases. Those children who had the habit of pica were more likely to consume multiple types of non-food substances. As many as 39% consumed soil, chalk, and wall paint. There were no cases who ate only pencil as a nonfood substance.  Table 3 shows the incidence of anaemia among the cases with pica and controls in the study. Proportion of cases with anaemia was significantly higher compared to controls (p=0.00005). Mean haemoglobin level was significantly lower in cases compared to controls (p=<0.001). Table 4 shows the comparison of plasma zinc levels in cases and controls.   Table 5 is a comparison of mean zinc levels among cases and controls. There was a significant association between pica and zinc levels (p<0.001).

Results
None of the controls had zinc deficiency, whereas out of the 46 cases enrolled in the study, 44 had zinc deficiency.  Table 6 shows the frequency of ingestion of nonfood substances. Table 7 shows the correlation of the duration of ingestion of non-food items with the mean zinc levels. The duration of ingestion of nonfood substances did not affect the mean zinc levels (p>0.05  Table 7 shows the correlation of the duration of ingestion of non-food items with the mean zinc levels. The duration of ingestion of non-food substances did not affect the mean zinc levels (p>0.05).  Table 8 shows the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of pica. Sensitivity of pica as a clinical marker to identify zinc deficiency is 100% which means that presence of pica could identify 100% cases of zinc deficiency. Specificity of pica as a clinical marker to identify zinc deficiency is 95.8% which means that absence of pica could exclude 95.8% cases without zinc deficiency among total normal cases. PPV of pica as a clinical marker is 95.7% which means that a case having positive history of pica will have 95% chances of zinc deficiency. NPV of pica as a clinical marker is 100% which means that a case with absence of pica will be without zinc deficiency on all occasions. Accuracy of pica as a clinical marker is 97%, which indicates that in 97% cases pica will accurately identify zinc deficiency.  20 . This suggests that the frequency and duration of ingestion of non-food substances do not seem to affect zinc levels significantly. In our study 95% of study group had anaemia compared to study by Miao D,et al 13 , where pica behaviour was associated with 2.4 times increased risk of anaemia. In our study zinc deficiency was present in 96% cases. Sensitivity was 100%, specificity 96%, PPV 96% and NPV 100%. Overall accuracy was 98% which suggests that pica as a clinical marker of zinc deficiency is likely to be sensitive as well as specific.
Thus, although it cannot be determined if pica is causally related to micronutrient deficiencies, it does suggest that pica is a clear marker of risk for these deficiencies, all of which have serious health consequences. Studies with larger sample size would help in further confirmation of the observation. It may be useful to supplement zinc in all cases of pica even if serum zinc levels are not done and clinical signs of zinc deficiency are not obvious considering the vital role of this micronutrient in growing age of the children when they are prone to higher incidence of infection and thus need any additional immune protective coverage.

Conclusions
In this study there was a definite association of zinc deficiency in children with the habit of pica, as the mean zinc level was significantly lower in those children which suggests that pica may be a useful clinical marker for zinc deficiency.