Besides seafood, rice products have the highest arsenic content. Long-term exposure to arsenic is linked to cancer
Many may be surprised that the large majority of cancers are related to environmental causes and genetic causes comprise a minority. Hence, the air we breathe, the food we eat and the water we drink – they all have a bearing on our health. Rice is a major food staple in this part of the world. Just recently, one of my patients, Mdm A, who had been eating a brand of rice which is less commonly consumed by the public but is available in high end supermarkets, was surprised that after consuming it for one year, her blood arsenic level was significantly elevated.
Arsenic in food: seafood and rice. Arsenic is a naturally occurring metal element that is present in water, air and soil, and is absorbed by some food crops as they grow. The forms of arsenic can be broadly divided into two categories; inorganic and organic. The term organic here refers to the chemical form and not the method of growing rice. While inorganic arsenic is the main toxic form of arsenic, the common form of organic arsenic (predominantly DMA) can also be toxic though organic arsenic compounds are generally considered to be of little toxicological significance.
The highest levels of arsenic are found in fish, crustaceans, and seaweed, but the arsenic is mainly organic and hence considered to have relatively minimal toxicological effect. Seafood aside, rice products have the highest arsenic content. Rice, being grown in flooded soils, is exposed to higher arsenic content in the soil and rice plants have evolved efficient mechanisms of capturing arsenic from soil solution. Hence, rice has higher levels of inorganic arsenic than other cereal foods.
Permissible levels of arsenic
Arsenic is classified by The International Agency for Research on Cancer, the European Food Safety Authority and the United States Food and Drug Administration (FDA) as a carcinogen based on the association between long-term exposure to arsenic with skin, lung and bladder cancers. Studies have linked high chronic (prolonged or long-term) exposure with adverse health effects in multiple organ systems including the stomach, kidneys, liver, and in coronary heart disease and diabetes.
Hence, in April 2016, the FDA proposed a limit of 100 parts per billion (ppb) for inorganic arsenic in infant rice cereal to reduce infant exposure to inorganic arsenic. In January 2016, the European Commission implemented regulations controlling the level of inorganic arsenic in rice products. For example, the inorganic arsenic content in rice destined for the production of food for infants and young children should not exceed 0.1 mg/kg wet weight.
Arsenic content in rice: high levels in rice bran and rice milk
The arsenic content in rice varies according to the type of soil where it is grown, the processing of the rice and the way of cooking the rice. In terms of the source of rice, in a publication in October 2015 in Environmental Science and Pollution Research journal, comparison of arsenic content from different sources of rice grains showed that on the whole, rice grains from United States of America had twice the level of arsenic of rice from Asian countries.
Generally, basmati rice is lower in arsenic than other kinds of rice whereas brown rice has a higher content of arsenic than white. Brown rice is higher in inorganic arsenic than white rice as arsenic is concentrated in the bran that is removed by milling to produce white rice. The amount of arsenic present in rice products also depends on the way the rice product is processed. Rice bran is composed of the hard outer layers of the rice grain and it contains a large amount of fibre. Although often thought of as a healthy fibre food product, one may be surprised to know that among the rice products, the highest arsenic concentration has been found in rice bran.
Rice cakes and rice crackers are popular snacks but the arsenic content can be higher than that in cooked rice. While consuming rice milk, be aware the arsenic content is higher than the amount that is generally allowed in drinking water. In the United Kingdom, children younger than 4½ years are advised against having rice milk because of arsenic concerns. The US Environmental Protection Agency, the European Union and the World Health Organization have set a level of 10 μg per litre for total arsenic concentrations in drinking water.
Reducing arsenic in rice by soaking
Studies by Mosley and Meharg from the United Kingdom showed that by soaking the rice overnight before cooking, using a ratio of 5 times as much water as rice, only 18 per cent of the arsenic remained in the rice. The time the rice is soaked in water allows the arsenic to leave the rice into the water. The following day, drain the water and rinse the rice thoroughly with fresh water. Add 5 parts of water to each part of rice and cook till the rice is tender. Do not boil the rice till it is dry. Drain the water again and rinse the rice with hot water to get rid of the cooking residual water.
However, if the rice is cooked till there is no more water or it is cooked with a rice cooker, the arsenic is reabsorbed into the rice. If the same ratio is used for cooking but not soaked overnight, 43 per cent of the arsenic remained in the rice.
Putting arsenic in rice in perspective
Before you decide to change to a no rice diet, you should know that the lung cancer and bladder cancer risk attributable to lifetime exposure to all rice products is a small portion of all cases of these cancers, at 39 cases per million people (10 cases/million bladder cancer and 29 cases/million lung cancer). This additional 39 cases are a small fraction of the 90,000 per million people who develop lung and bladder cancer over a lifetime from all causes.
Rice is not the only source of arsenic in food. A 2014 European Food Safety Authority (EFSA) report stated that the main contributor of inorganic arsenic, except for infants and toddlers, was grain-based processed products (nonrice-based). In the ESFA report, other important contributors to the overall intake in all age classes were rice, milk and dairy products and drinking water. Food experts do not consider the consumption of rice products a few times a week a health risk, and rice continues to be a part of the international recommendations on food.
Things to note
Remember the following when making decisions on rice:
- Do not be fooled by “organic” rice labels – they have no bearing on the arsenic content.
- White rice has a lower content of arsenic compared to brown rice.
- Asian sources of rice have lower arsenic content.
- Young children below 5 years should avoid rice milk and reduce rice-based snacks.
- Apparently “healthy” rice bran has the highest arsenic content among rice products.
- Cooking rice the right way can minimise the arsenic to negligible levels.
- Eating the “right” rice will have no significant adverse impact on your health. Hence, there is no need to give up your chicken rice, nasi biryani and nasi lemak!
Dr Michael Lim
MWH Heart Stroke and Cancer Centre
MBBS, MRCP (UK), M Med (Int Med), FAMS (Cardiology), FRCP (Edin)
THE BUSINESS TIMES WEEKEND 9 NOVEMBER 2019