Abstract
Modern dietary recommendations since the 1960s, such as the Mediterranean diet, have recommend a more plant-based diet, rich in fruits, vegetables, whole grains, nuts, and olive oil along with a moderate intake of dairy products (such as yogurt and cheeses), eggs, poultry, and fish and minimal, if at all, red meat. Documented health benefits from such diets include reduced incidence of cardiovascular disease, strokes, type 2 diabetes, and obesity. More recent recommendations have included limiting intake solely to plant-based products (i.e., vegan diets) or eliminating the intake of any poultry or fish products, whereas continuing a varied intake of eggs and dairy products, in what is termed lacto or lacto-ovo vegetarian diets. Not surprisingly, the popularity of vegan/vegetarian diets have doubled in the past decade and are now estimated to be as high as 20% of the meals eaten by adults.
Neufingerl and Eilander 1 recently summarized the results of 141 published studies that assessed the nutrient status of adults on such diet. They noted that although “protein intake was lower in people following plant-based diets compared to meat-eaters, it was well within recommended intake levels. While fiber, polyunsaturated fatty acids (PUFA), folate, vitamin C, E and magnesium intake was higher; eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) intake was lower in vegetarians and vegans as compared to meat-eaters. Intake and status of vitamin B12, vitamin D, iron, zinc, iodine, calcium and bone turnover markers were generally lower in plant-based dietary patterns compared to meat-eaters. Vegans had the lowest vitamin B12, calcium and iodine intake, and also lower serum iodine levels and lower bone mineral density.”
In particular, both the low level of maternal iodine intake and of serum levels of vitamin B12 have been documented to be a cause of neurological and hematological diseases. 2 More recently clinical manifestation of B12 deficiencies have also been documented in infants exclusively breastfeeding from mothers on such plant-based diets. 3 The major concern regarding these infants has been the issue of the irreversibility of the brain damage and the negative long-term effect of “failure to thrive” condition developing at this critical infant developmental stage. 4
This issue of Breastfeeding Medicine includes a report of Pawlak and colleagues summarizing the results of a study of the iodine levels in breast milk from mothers on varied diets. In this small and somewhat preliminary study, they documented that most samples of breast milk from vegans and vegetarians contained a lower breast milk iodine concentration than what is recommended by the U.S. National Academy of Medicine as an adequate intake for infants 0–6 months. The study did not measure iodine levels or thyroid function in the infants and did not report on the clinical status of the infants.
However, as it is well known that an adequate iodine intake is critical for normal infant thyroid function, which in turn is necessary for normal growth and development in the critical first months of the infant's life this concern is legitimate. Clearly larger studies are necessary that must include not only measures of iodine intake, but also breast milk iodine content, infant thyroid function, and neurodevelopmental function. Data from such studies will then become the basis of recommendations as to what should be the proper mineral and vitamin supplementation of plant-based diets.
It should be thus clear then that the potential negative effect resulting from infants nursing from mothers whose diet is limited to plant-based foods should be of major concern. As infantile hypothyroidism is at times very subtle and without any specific clinical manifestations it behooves clinicians to be alert and to more routinely assess the mothers' diet to identify possible critical dietary deficiencies in the breastfeeding infant, particularly of micronutrients (iodine iron) and vitamins (B12 and D). Such diets should be a red flag that we cannot ignore. 5