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Prenatal phthalate exposure linked to increased risk of childhood asthma

Allergy, Asthma, Infant and Children | December 24, 2014 | Author: The Super Pharmacist

Children, infant, Asthma

Prenatal phthalate exposure linked to increased risk of childhood asthma

You must have noticed how plastic items become inflexible and fragile as they age. Items that were once so resilient just break, crumble or shatter on bending. How does this happen? This isn’t metal so corrosion is ruled out, or wood, so termites can’t be a clue. The mystery is removed when we learn the difference between plastic and plasticisers. It turns out that plasticisers are what make plastic flexible and durable. Plasticisers can make up to 20 to 50% of plastics by weight. Plasticisers are not chemically bonded with the plastic and leach out of it over time. Without the plasticiser, the plastic changes properties from being the flexible, durable stuff it is known to be, to a rigid, fragile material.

Phthalate is the Chief Plasticiser

The most predominant form of plasticiser is phthalate. Almost 90% of phthalate production is meant for use as plasticiser added to plastic. The chief form of plastic that incorporates phthalates is polyvinyl chloride (PVC). Chemically, phthalates are esters of phthalic acid and higher the molecular weight, greater the longevity. Although low molecular weight phthalates are faster to leach out of plastics, they have traditionally been more commonly used. They are now being replaced by high molecular weight phthalates and non-phthalate plasticisers. Some of the frequently used phthalates are

  • Diethylhexyl phthalate (DEHP)
  • Di-n-butyl phthalate (DnBP)
  • Diethyl phthalate (DEP)
  • Butyl benzyl phthalate (BBzP)
  • Diisononyl phthalate (DINP)
  • Diisodecyl phthalate (DIDP)

Phthalate is the Chief PlasticiserWhen you want examples of household items that contain a phthalate, what you will find more challenging is to name items that don’t. Phthalate is ubiquitous. It’s present in just so many items of daily use. Here is a brief list:

  • Cosmetics (DnBP, DEP)
  • Toys (DINP)
  • Construction material (DEHP)
  • Car parts (DIDP)
  • Vinyl flooring (BBzP)
  • Medical devices (DEHP)

Health Hazards of Phthalates

When the phthalate in a plastic leaches out, it just doesn’t disappear. It either mixes into the room air or its particles become a component of house dust. Phthalate that leaks out of water pipes and tubing can get into the water supply. These characteristics make phthalate an environmental and household pollutant. We can inhale phthalates, eat or drink them with food or water, or absorb them through our skin. In this modern world of universal plastic use, there is probably no one without phthalates in his/her body; the amount though can vary.

When the ubiquitous presence of phthalates in our environment and homes and our extensive exposure to them became well-recognised, researchers embarked on finding out how they affect us. The effects of phthalate were studied in children and adults exposed to it, and in children exposed to it prenatally. Some of the associations that emerged are presented:

Exposed Adults

  • Antiandrogenic effects
  • Carcinogenic
  • Breast cancer
  • Insulin resistance and obesity
  • Poor sperm quality in men

Exposed Children

  • Increased asthma attacks
  • Attention Deficit Hyperactivity Disorder (ADHD)
  • Precocious puberty

Children with Prenatal Exposure

  • Behavioural problems
  • Asthma
  • Undescended testis in boys
  • Decreased anogenital distance in boys

Health Hazards of PhthalatesHowever, as will be explained below, there is a difference between association and causation.

While the above effects have been associated with phthalate exposure in some studies, there is no conclusive evidence of causation yet and further research is required.

In the meantime, the best approach would be to minimise our exposure to phthalates as much as possible.

Prenatal Phthalate Exposure and Childhood Asthma

The focus of our current discussion is to examine if prenatal phthalate exposure is linked to increased risk of childhood asthma. They aren’t many studies that have tried to explore this directly. One recent study, whose results are better known and have spotlighted the problem, was conducted by a team of researchers from Columbia University, New York, with Robin Whyatt as the lead author. The study enrolled 300 women while they were pregnant. Urine phthalate metabolite levels were checked for the women during the 3rd trimester of their pregnancy as an indicator of phthalate exposure. Higher levels meant higher prenatal exposure for the child. Urine phthalate metabolites were then checked in the children’s urine samples at ages 3, 5 and 7. Almost a 3rd of the children developed clinically diagnosed asthma between ages 5 and 11. A comparison was then made between the level of prenatal phthalate exposure and the risk of developing childhood asthma. The results were staggering. Children with high levels of prenatal phthalate exposure were more than 70% more likely to develop childhood asthma as compared to children with low levels of prenatal exposure.

Association vs. Causation

Although Whyatt and the team’s research suggests a connection, we have to understand the difference between association and causation before we reach any conclusions. To put it simply, two factors are associated if they are changing at the same time. In the above study, when you see an increase in prenatal phthalate exposure, you simultaneously notice an increase in childhood asthma. An association has been discovered. Causation on the other hand is scientifically proven evidence that a change in one factor will lead to a change in the other. The study doesn’t profess to prove that. For example, a research may conclude that plastics become weaker, inflexible and more brittle with the passage of time, but this is an association. Leaching phthalates are the causation and if a chemical process is discovered that permanently binds plasticisers to plastics, the observed association will disappear. Similarly, the above study points towards an association and only when the elaborate biochemical mechanisms by which phthalates induce pathological changes leading to asthma are fully understood, can we confirm this to be a causation. However, despite all that, an association is often enough reason to level up precaution.

Factors that Point to a Link

Factors that Point to a LinkEven though there aren’t many studies directly exploring the link between prenatal phthalate exposure and childhood asthma, there are many others which show that phthalate exposure in general and prenatal phthalate exposure in particular give rise to numerous health effects in children. These have been listed above and lend credibility to the fact that the specific link we are talking about is real.

Factors that Point Away

There are some characteristics of the study that lessen the applicability of its results to the general population and restrain us from jumping to conclusions. The sample size was relatively small and very select, which means extrapolating the results to the whole population would be fraught with error; urine phthalate metabolites were checked only once during the 3rd trimester, which is not reflective of exposure throughout pregnancy, especially when it is known that levels fluctuate; and the role of confounding factors (other factors that can affect results) has to be further investigated.

Concluding Remarks

A link between prenatal phthalate exposure and increased risk of childhood asthma has been observed but more research is required to establish it beyond doubt. Talking about phthalates in general, the American Chemical Council states on its website:

‘Phthalates have been thoroughly studied and reviewed by a number of government scientific agencies and regulatory bodies world-wide and these agencies have concluded that phthalates used in commercial products do not pose a risk to human health at typical exposure levels. Information collected by the Centers for Disease Control and Prevention over the last 10 years indicates that, despite the fact that phthalates are used in many products, exposure is extremely low—significantly lower than any levels of concern set by regulatory agencies.’

Regulatory agencies are acknowledging the health hazards of some of the phthalates and restrictions are emerging.

Toy manufacturers and cosmetics producers are reducing or removing potentially harmful phthalates from their products voluntarily as well as under regulations. Other industries and regulatory agencies are bound to follow as further research increases public awareness about the health effects of phthalate exposure.

Precautionary principle

The precautionary principle emphasises that if an action or policy carries a suspected risk of adverse effects to people, it is better to avoid it even if there is no conclusive evidence of causation. Sticking to this principle, our conclusion in this matter will be to minimise exposure to phthalates as much as possible, especially during pregnancy.

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References

Swan SH. Environmental phthalate exposure in relation to reproductive outcomes and other health endpoints in humans. Environmental Research. 2008; 108: 177–184.

López-Carrillo L, Hernández-Ramírez RU, Calafat AM, Torres-Sánchez L, Galván-Portillo M, Needham LL, Ruiz-Ramos R, Cebrián ME. Exposure to phthalates and breast cancer risk in northern Mexico. Environ Health Perspect. 2010; 118(4): 539–44.

Bornehag CG, Nanberg E. Phthalate exposure and asthma in children. Int J Androl. 2010; 33: 333–345.

Kim B.N., Cho S.C., Kim Y., Shin M.S., Yoo H.J., Kim J.W., Yang Y.H., Kim H.W., Bhang S.Y., Hong Y.C. Phthalates exposure and attention-deficit/hyperactivity disorder in school-age children. Biol. Psychiatry. 2009; 66: 958–963.

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