1. Troubled waters
The fish we eat, such as tuna and salmon, all contain small amounts of mercury – a pollutant that can be highly toxic to our nervous systems.
As a medical doctor, I’m conscious about what I eat. And a diet that includes fish comes with some great health benefits. Seafood is a good source of protein and, unlike many meats, it's typically low in saturated fat. It’s also a great source Vitamin D and Omega-3 – a type of fatty acid we can’t live without.
However some fish contain more mercury than others. I want to know how mercury can harm my body and whether I should limit the type and amount of fish I eat.
4. CLICKABLE: Harmful effects
Click or tap the image below to discover how high mercury levels can damage our nerves, brain and heart.
This content uses functionality that is not supported by your current browser. Consider upgrading your browser.
5. Catch of the day
Some types of fish contain much more mercury, on average, than others. However, mercury levels can vary between populations of the same species depending on where they reside and migrate.
6. Radha's review
The Minamata disaster shows high doses of methylmercury can cause irreparable damage to our bodies.
However the effect of regular, low doses in a typical diet containing fish is less well understood. That’s partly because seafood also contains beneficial substances such as Omega-3 fatty acids, which are good for the nervous system and may help counteract the adverse effects of methylmercury.
Pregnant women and babies
For example, there is evidence methylmercury can inhibit the development of an unborn child’s nervous system. However, the Omega-3s in fish may also promote the development of a baby’s brain.
That's why the NHS advises pregnant and breast-feeding women to continue eating fish – but to limit the amount and type they consume (click the link below for more information).
It's also important to note it takes months to excrete the methylmercury absorbed from fish. This means a human foetus can be exposed to some of the mercury consumed by the mother before she falls pregnant.
Non-pregnant adults and children
Studies show a clear relationship between high, frequent fish consumption and the amount of mercury in our bodies. Yet defining the amount of fish we should eat to avoid harm is complex because methylmercury affects everyone differently depending on their weight, age and genetics (Silbernagel S. et al, 2011).
Many dietary advisories advocate that the benefits of eating fish generally outweigh the risks of mercury exposure. For example, although some studies found that heart disease increases with mercury exposure, others have shown fish oils may reduce the risk of cardiac death (Mozaffarian D., 2009).
The Food Standards Agency (FSA) suggests that eating species relatively low in mercury is the most effective way to minimise excessive exposure. Fish that are low in mercury but high in Omega-3s include Atlantic mackerel, salmon and sardines.