An Update on Pica: Prevalence, Contributing Causes, and Treatment

In addition, ethnic differences occur in pica. For example, most cases of lead poisoning in New York were in Hispanic children, and the incidence increased in summer when vitamin D elevation by sunlight-induced synthesis may promote increased lead absorption.^14,15 Pica is endemic among sedentary aborigines in Australia, where clay has been eaten as a fertility food.^16,17 In Turkey, young women were encouraged to eat clay to enhance their fertility.¹⁸ Similar ideas shared in black culture encouraged pregnant females, both in Africa and later in the United States, to eat various types of clay to enhance childbearing.¹⁹ However, contemporary health education and availability of medical care have diminished these practices.

Mechanisms
The theory that the eating of non-nutritive substances is a need- determined behavior is supported by studies of food selection in young infants.²⁰ Nutrient deficiencies and medical consequences such as iron deficiency, lead intoxication, growth and cognitive impairment, and in-testinal obstruction are frequently associated with idiosyncratic dietary habits.^21,22

Recommendations for dietary alteration and the empirical use of iron preparations as treatment appeared before iron deficiency was proposed as a factor in the development of pica.²³ Frustration of oral drive as a cause of fixation is not seen in the pica group.

Studies of food selection by Rolls²⁴ suggest 2 adaptive mechanisms in the control of eating: (1) sensory-specific satiety, in which a person's perception of a specific food as pleasant decreases with increasing intake of that food, while other foods not eaten increase in pleasantness as a function of time since last eaten, and (2) neophobia, the avoidance of food not in a person's current food repertoire. Both mechanisms have an adaptive value. Sensory-specific satiety leads to increased variety, and neophobia ensures against eating possibly dangerous or nonnutritive foods. Perhaps both mechanisms are impaired or inoperative in persons with pica.

The role of iron deficiency
Pica has been associated with occult iron deficiency, which resulted in the sudden appearance of eating nonnutritive objects such as match heads²⁵ and raw potatoes.²⁶

The most compelling argument for the association of pica with iron deficiency is suggested by the studies on pagophagia (compulsion to eat ice). Reynolds and colleagues²⁷ found pagophagia associated with low serum iron levels. Iron supplementation abolished pagophagia before correcting the anemia. In addition, Coltman²⁸ reported cessation of pagophagia in 19 of 25 women with iron deficiency after iron supplementation for 5 days with intramuscular injection and 11 days with oral iron administration.

A critical review of clinical reports reveals that most authors verify the efficacy of iron supplementation in abolishing food and nonfood pica associated with iron deficiency states. This suggests a common central pathway such as mediation by decreased CNS dopamine(Drug information on dopamine) neurotransmission, which has been reported to be a specific result of iron deficiency.^29,30

Several studies suggest CNS neurochemical iron-dependent appetite regulation.^31-33 Systematic iron deficiency results in no predictable alteration of iron-dependent enzymes or changes in CNS catechol neurotransmitter metabolites. Youdim and colleagues³⁴ linked decreased brain iron specifically to decreased dopamine D² receptors and consequent reduction of several CNS dopamine-driven behaviors.

On the other hand, some study findings suggest that pica may be a cause of iron deficiency in which the nonnutritive substance (eg, clay, starch) interferes with the dietary intake or absorption of iron.^35-37 Further research on the neurobiological basis of pica is clearly desirable.

Pica may be a presenting symptom that can alert the clinician to anticipate a possible iron deficiency and, thus, the need to pursue a careful differential diagnosis.³⁸ Pica frequently ceases after a few days of iron supplementation, which supports the role of iron loss in initiating and promoting pica.