Eating fish and mercury exposure

Should I eat fish if I’m breastfeeding?

Mercury is a heavy metal that is toxic. Among other effects, it can permanently damage the brain and nervous system. Individuals working in certain industries may be exposed to it. Fish is part of a healthy diet, but some types of fish have higher levels of mercury and possibly other heavy metals. These include many larger fish such as swordfish, escolar, marlin, Chilean sea bass (toothfish), and orange roughy. More information about specific fish is available on the websites of some government and non-governmental organizations. Mercury can also be present in infant formula the foods that a baby eats. Unless a mother has very high levels of mercury in her body, the benefits of breastfeeding outweigh the risk of mercury exposure. Mercury levels in the body are measured by means of a blood test.

A) Describing mercury

Mercury is a heavy metal that occurs naturally in the environment and is also dumped into our water, soil, and atmosphere by industry. Bacteria combine mercury with carbon and hydrogen to form methyl mercury. It then enters the food chain and becomes more concentrated (biomagnification) as it moves up the chain.

Human activities have nearly tripled the amount of mercury in the atmosphere and the atmospheric burden is increasing 1.5 percent per year (Clifton 2007). The largest sources of mercury pollution are small-scale gold mining, the burning of coal, and non-iron metal and cement production.

Mercury remains in use in batteries, fluorescent lamps, cosmetics, pesticides, thermometers, and dental amalgams (Minamata Convention 2013). Mercury remains common in illegal skin-lightening products (Desmedt 2016; Hamann 2014).

The main route of mercury entering our bodies is by eating certain large fish that contain methyl mercury. Individuals working in the industries described above can absorb mercury in the workplace or it can be taken in through the skin.

The Minamata Convention which entered into force in August 2017 aims to reduce and stop the use of mercury and mercury compounds (Minamata Convention 2013). 

For more information about mercury and other environmental risks in your area, please contact your local health agencies.

B) The effect of mercury on health

Mercury poisoning can affect every system in our bodies. In particular, mercury can damage a baby’s brain and impair its development. The exact effects depend on which type of mercury, how much mercury is involved, how it enters the body, and how long it is present  (Rice 2014). In very large amounts, it can be lethal. Mercury levels are measured by the use of blood tests.

Mercury poisoning was reported as long ago as 200 BCE with the death of the Chinese emperor Qin Shi Huang. Over the years, mercury poisoning has caused (Rice 2014):

  • “Mad Hatter disease” among hat makers from the 1600s to the early 1900s. 
  • Hunter-Russell syndrome among English seed-packing workers in the 1930s.
  • Minamata disease in Japan in the 1950s.

C) Mercury in fish

Fish is part of a healthy diet, but some species have higher levels of mercury and possibly other heavy metals (Bradley 2017; Vu 2017). In general, larger fish contain more mercury. Some examples of fish that are likely to have higher levels of mercury include (Karimi 2012; Rice 2014):

  • Swordfish
  • Escolar
  • Marlin
  • Orange roughy
  • Shark
  • Albacore (white) tuna
  • King mackerel
  • Tilefish
  • Whitecroaker/Pacific croaker
  • Chilean sea bass (toothfish)
  • Grouper

Whales, dolphins, and other sea mammals are known to have high levels of mercury (Endo 2003; Sundseth 2015). 

Identifying mercury-containing fish may be difficult as they may have different names or be deliberately mislabelled (da Silva 2019).

Many government and non-government organizations have more information and guidelines online about the consumption of fish by breastfeeding mothers and their children.

D) Concerns about mercury and breastfeeding

Babies can be exposed to mercury before birth and to a lesser degree, through breastfeeding (Dorea 2004). Unless a mother has very high levels of mercury in her body, the benefits of breastfeeding outweigh the risk of mercury exposure (Rebelo 2016). It is possible for infant formula to be contaminated with mercury (Dorea 2004).

References

Bradley MA, Barst BD, Basu N. A Review of Mercury Bioavailability in Humans and Fish. Int J Environ Res Public Health. 2017 Feb 10;14(2):169

Clifton JC 2nd. Mercury exposure and public health. Pediatr Clin North Am. 2007 Apr;54(2):237-69, viii
 
da Silva CF, Daneluz CM, Camacho-Oliveira RB, et al. DNA Barcode reveals mislabelling in the identification of marine fish swimming bladders for commercialization. Forensic Sci Int. 2019 Jun;299:41-43
 
Desmedt B, Courselle P, De Beer JO, et al. Overview of skin whitening agents with an insight into the illegal cosmetic market in Europe. J Eur Acad Dermatol Venereol. 2016 Jun;30(6):943-50
 
Dorea JG. Mercury and lead during breast-feeding. Br J Nutr. 2004 Jul;92(1):21-40
 
Endo T, Hotta Y, Haraguchi K, et al. Mercury contamination in the red meat of whales and dolphins marketed for human consumption in Japan. Environ Sci Technol. 2003 Jun 15;37(12):2681-5

Hamann CR, Boonchai W, Wen L, et al. Spectrometric analysis of mercury content in 549 skin-lightening products: is mercury toxicity a hidden global health hazard? J Am Acad Dermatol. 2014 Feb;70(2):281-7.e3
 
Karimi R, Fitzgerald TP, Fisher NS. A quantitative synthesis of mercury in commercial seafood and implications for exposure in the United States. Environ Health Perspect. 2012 Nov;120(11):1512-9
 
Minamata Convention on Mercury (Minamata Convention). Geneva: United Nations Environment Programme; 2013
 
Rebelo FM, Caldas ED. Arsenic, lead, mercury and cadmium: Toxicity, levels in breast milk and the risks for breastfed infants. Environ Res. 2016 Nov;151:671-688
 
Rice KM, Walker EM Jr, Wu M, et al. Environmental mercury and its toxic effects. J Prev Med Public Health. 2014 Mar;47(2):74-83

Sundseth K, Pacyna JM, Banel A, et al. Climate change impacts on environmental and human exposure to mercury in the arctic. Int J Environ Res Public Health. 2015 Mar 31;12(4):3579-99

Vu CT, Lin C, Yeh G, et al. Bioaccumulation and potential sources of heavy metal contamination in fish species in Taiwan: assessment and possible human health implications. Environ Sci Pollut Res Int. 2017 Aug;24(23):19422-19434