Public Health Implications of Recent Breastfeeding Research Regarding Cannabis Use and Risk of Childhood Obesity

Abstract

Introduction

Published research on the subject of breastfeeding has dramatically increased in the past decade. Surveying PubMed with the key words of “breast milk,” “lactation,” “and breastfeeding” has noted an increase of published peer reviewed articles of 53% since 2006. The majority of the articles focus on issues of biology of breast milk and process of lactation, or programs that promote and support breastfeeding in the mother infant dyad. A minority address specific issues of public health policy. Even less have been the publications of data that potentially have subsequent major public health implications.

The goal of this presentation is to review selected recently published articles whose results, in my opinion, will have major impact on our knowledge and understanding of the societal context of breastfeeding and thus ultimately affect or modify future public health policies and guidelines.

Methodology

English language peer reviewed articles published and cited in Pub Med in the period between January 2017 and June 2018 were reviewed. The selection was personal with no ranking per se as to quality or Citation Index score. Only human studies were reviewed.

Results

Two subjects were chosen: Breastfeeding and cannabis use and impact of breastfeeding on the risk of childhood obesity.

Breastfeeding and cannabis

As of June 2018 in the United States of America 30 states and the District of Columbia (DC) have authorized the legal use of Cannabis (marijuana) for medicinal purposes, while eight states and DC have legalized recreational use. In a seemingly paradoxical and contrarian fashion the U.S. Federal government has continued to designate cannabis as Schedule 1 controlled substance. Such substances are defined as “having no accepted medical use… lack accepted safety …and have a high potential for abuse”. Furthermore, such a designation leads to administrative restrictions that severely limit the feasibility of performing therapeutic trials or obtaining federal financial support for clinical and epidemiological studies.

To date, there are very limited data as to the use of cannabis during pregnancy and while breastfeeding. The largest population study is a sample of 170,000 households with children under the age of 18 who were surveyed as part of the United States National Survey on Drug Use and Health.¹ The study compared the prevalence of cannabis use in the year 2015 as compared to the results of a comparable study performed in 2002. In 2015 the prevalence of cannabis use rose to 6.8% from 4.9%. Of interest cigarette smoking decreased in this period from 27.6% to 20.7%. Among smokers the prevalence of cannabis use rose from 11% in 2002 to 17.4% in 2015 (Table 1). Limitations of this study were that no data as to breastfeeding were collected and no information was provided regarding the ages of the children, for example, how many were infants who were potentially breastfeeding.

Table 1.

Prevalence of United States Cannabis Use

Year	Cannabis use total population (%)	Cigarette use total population (%)	Cannabis use any smokers (%)	Cannabis use daily smokers (%)
2002	4.9	27.6	11	0.7
2015	6.8	20.7	17.4	1.6
	Increase 39%	Decrease 27%	Increase 58%	Increase 130%

Adapted from Goodwin et al.¹

Another study sample was of 3,207 mothers who responded to the Colorado Risk Assessment Monitoring System and who self-reported on cannabis use.² This report was from a state that had already legalized marijuana for recreational use. Prevalence of self-reported cannabis use during pregnancy was reported as 5.7% and was 5% while breastfeeding.

Outcome data were not presented from the National study. The Colorado study did report that there was a 50% increase in the frequency of low birth weight (<2,500 g) infants. A similar report of an increased number of small for gestational age (SGA) infants has been previously reported by Warshak et al.³ in a study of over 6,000 mothers. Metz et al.⁴ studied a population of some 1,610 and did not note an increase in SGA infants, but, did document a significant increase in composite neonatal death or morbidity. No increase in prematurity was noted in any of the studies.

Unfortunately, none of the studies reported any data on the potential effect (short or long term) on infants nursing from mothers who indulge in cannabis or exposed to household secondary cannabis smoke.

The pharmacokinetics of inhaled cannabis into breast milk has as yet to be fully delineated. Baker et al.⁵ in a well-designed study noted that a nursing infant would receive the equivalent of 2.5% of the maternal dose from a single smoke of cannabis cigarette. While this figure sounds reassuring as to infants exposure, given the half-life of cannabis, its fat solubility and slow infant excretion rate, the effect of repeated exposure is of concern. Unfortunately, there are inadequate data to reach any conclusion. Furthermore, cannabis decreases prolactin levels and oxytocin production potentially decreasing milk production and normal let down reflex process.

What are the public health implications of these reports? It is clear that increased legalization of recreational marijuana will inevitably lead to an increased prevalence of marijuana use by nursing mothers. Anecdotal reports of a prevalence use well over 10% are already common. Given the documented adverse effect of marijuana use during pregnancy and the theoretical negative effects on the nursing infant what should be the public health recommendation. Clearly all efforts should be made to counsel mothers who are pregnant to categorically desist from cannabis use. The more complex issue is what to recommend to the nursing mother. The consensus of the Academy of Breastfeeding Medicine consultants is that combined maternal and infant health benefits of breastfeeding outweigh the theoretical risk of cannabis exposure through the breast milk. Thus, our advice would be to continue breastfeeding and to minimize as much as possible cannabis use.⁶

As legalized recreational cannabis becomes more ubiquitous serious question whether there should be mandatory labeling of such commercial products in a way comparable to what exists for alcohol or cigarettes. Yes, cannabis can be deleterious to the health of your fetus or nursing infant and the public should thus be properly warned. If we require it for alcohol and cigarettes why not for cannabis?

In addition, with a prevalence of 10% or more in breastfeeding mothers, regulations and guidelines regarding human milk banks should be reviewed. At a minimum there should be a prohibition of accepting donor milk from mothers who are cannabis users. Given the unreliability of self-reporting and the indiscriminate availability of cannabis the more appropriate approach is that all donor milk (be it peer to peer and from recognized milk banks) be routinely screened for cannabis. Surely such milk that is positive should be categorically prohibited from being used in our newborn intensive units especially for our vulnerable preterm infants.

Breastfeeding and the risk of childhood obesity

Childhood overweight and obesity continues to be a major problem in the developed world. A recent survey in the United States⁷ has documented a steady rise in the prevalence of both overweight and obesity reaching a level of 35.1% and 26.4% respectively in the years 2015–2016 (Table 2).

Table 2.

United States Childhood Overweight/Obesity “Epidemic”

Years	Overweight (%)	Obese (%)
1999–2000	28.8	17.5
2005–2006	30.1	22.2
2011–2012	32.0	24.8
2015–2016	35.1	26.4

Adapted from Skinner et al.⁷

Bell et al.⁸ recently reported the results of a study that attempted to discern what impact breastfeeding in infancy has on a toddler's weight. The focus of the study was to determine whether the key factor was the duration of breastfeeding or the age when solid food were added to the infant's diet. One should remember that the current recommendations of the American Academy of Pediatrics⁹ are for mothers to exclusively breastfeed for about 6 months and continue breastfeeding along with complimentary foods for 1 year or longer as mutually desired by the infant and mother. The World Health Organization recommends 6 months of exclusive breastfeeding and continuing with breastfeeding up to 2 years and beyond along with complimentary foods. Of interest the potential advantages of early introduction of solids after 3–4 months has been reported by Perkin et al.¹⁰

Given these reports answering the question of what is the impact on the pattern on weight gain in childhood is not moot. To that end Bell et al.⁸ prospectively followed 900 term infants documenting duration of breastfeeding and age of introduction of solid foods into their diet. As noted in Table 3 infants who continued to breastfeed for more than year had a significant reduction in being overweight at ages 24–26 months. Continuing to breastfeed for only up to 1 year had no impact. Additionally, the age of introduction of solid food had no impact on weight gain. The data were analyzed by multiple regression and these results were independent of maternal age, socioeconomic status, infant birth weight, mode of delivery, or maternal smoking.

Table 3.

Adjusted Odds Ratio for Being Overweight at 24–36 Months

	AOR	CI	p-Value
Breastfeeding duration (weeks)
<17	1.0	—	—
17–25	0.8	0.3–1.70	0.56
26–51	0.8	0.46–1.47	0.51
>52	0.49	0.27–0.90	0.02^*
Age of solid food introduction (weeks)
<17	1	—	—
17–25	0.94	0.57–1.54	0.80
>26	0.56	0.20–1.55	0.26

Adapted from Bell et al.⁸

p < 0.05 significant.

AOR, adjusted odds ratio; CI, confidence interval.

How does continuing breastfeeding for more than a year confer an advantage of minimizing the risk of being overweight as a toddler? At least four mechanisms have been postulated: (1) The composition of breast milk, especially its lower protein content minimizes the stimulation of infant growth factors. (2) Breast milk hormones such as leptin, ghrelin, and adiponectin regulate the infant's appetite and metabolism. (3) The different gut microbiome in breastfeeding infants modifies gastrointestinal absorption patterns. (4) Breastfeeding infants develop self-regulation mechanism and thus minimize overfeeding by caretakers.

These data have to be evaluated in the context of what is both being recommended by public health authorities and what is the reality of breastfeeding patterns. The Healthy Peoples 2020 Objectives¹¹ set a goal of “any breastfeeding” at 6 months of 60.6% and at 12 months of 34.1%. The actual current rate is 51.8% and 30.2%. These data confirm that only a very small proportion of mothers in the United States actually breast feed for a year, let alone for more than 1 year. Clearly if one is truly concerned regarding the overweight/obesity epidemic and the long-term implication for childhood and adult health one should consider reevaluating both the breastfeeding goals and formal public health recommendations. Simply put, if duration of breastfeeding is a key preventive health process then the WHO recommendation of 2 years breastfeeding should become the standard and not the implied 1 year of the American Academy of Pediatrics and the “goals” need to be revised. A “goal” that only one-third of mothers will provide the protective benefit to their infants is shortchanging the next generation and expecting too little from concerned mothers!

References

Goodwin

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10.

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11.

Breastfeeding Report Card 2016. National center for chronic disease prevention and health promotion. Available at https://cdc.gov/breastfeeding/pdf/2016breastfeedingreportcard.pdf (accessed July 16, 2018).