Low Riboflavin and Methionine Diets Linked to Lung Cancer
Researchers have determined that deficiencies in two common food nutrients – riboflavin and methionine – are linked to higher rates of lung cancer among women.
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Diets and lung cancer studied
The researchers, from the Vanderbilt University School of Medicine working at the VU’s Vanderbilt-Ingram Cancer Center, conducted a study that followed 71,267 non-smoking women for over eleven years. The research looked into the potential associations between B vitamins and cancer, as well as amino acids – the building blocks for protein.
The subjects’ dietary intakes were measured using personal interviews and questionnaires, along with twice-a-year personal follow-ups. The researchers compiled this data against cancer cases taken from the Shanghai Cancer Registry and the Shanghai Vital Statistics Registry.
The research found that those women who ate fewer foods containing riboflavin had 38% higher incidence of lung cancer during the eleven-year period. In addition, those who ate fewer foods containing the amino acid methionine had a 22% increase in lung cancer incidence during the same period.
How riboflavin is lost
The difference is significant because processing robs many foods of their riboflavin content. This is especially true when it comes to milling rice and cereal grains, which carry significant levels of riboflavin (or vitamin B2).
Riboflavin is light sensitive, so when the whole grains or rice are dehulled and/or degermed, much of the photosensitive riboflavin is typically lost. While some grains and rice are fortified with B vitamins after processing – riboflavin is often not included in fortification because riboflavin is yellow-orange colored, and this is unappealing to those who prefer their white rices and white flours, well, white. (Riboflavin also makes our pee turn yellow after taking multivitatmins.)
The Western-influenced dehulling and bleaching of rice to white in Asia – after thousands of years of healthily eating brown rice – became implicated in deficiency disorders such as beriberi and pellagra. Beriberi has been linked to a deficiency in thiamine and pellagra is a deficiency in niacin – two other B vitamins lost when rice and other grains are dehulled and processed. In addition to riboflavin, dehulling and processing of rice also damages thiamine and niacin content, as well as the rice’s natural content of magnesium, iron, folacin, vitamin E, vitamin B6 and all-important important fiber. White rice will typically have less than a quarter of the fiber content (about 3.2 grams per serving) of brown rice. Deficiency in riboflavin is called ariboflavinosis.
This is also probably why junk food diets are linked to lung cancer.
Other sources of riboflavin include wheat bran (whole wheat), pulses, yeast, leafy green vegetables, cheese and milk.
Problems with too little methionine
The researchers also found lung cancer was associated with the amino acid methionine. Methionine is a critical amino acid because it contains what is referred to as a methyl group. Methyl groups are important components in the body’s ability to detoxify itself. Methyl groups are donated to unstable toxins in order to stabilize them, so the immune system can escort them out of the body and/or break them down into less dangerous molecules. One of the processes here is the S-adenosylmethionine (SAM) conversion pathway, which donates methyl groups that help protect cells against DNA mutation.
Some of the best sources of methionine are sesame seeds, cereal grains (brans), oats, peanuts, almonds, lentils, brazil nuts, and other types of seeds. Brown rice also contains a reasonable amount of methionine. As cereal brans are often a large part of traditional diets, deficiency in methionine can easily take hold when the bran is removed from the grains to make white flours.
One of the key issues about both of these nutrients within the context of the study is that their association with cancer was related to their inclusion in foods – and increased dietary doses did not compute to greater lung cancer prevention. “There was no dose-response relation,” the researchers commented. This means that more is not necessarily better, and by far the safest ways to get our nutrients is to eat whole foods with minimal processing.
Takata Y, Cai Q, Beeghly-Fadiel A, Li H, Shrubsole MJ, Ji BT, Yang G, Chow WH, Gao YT, Zheng W, Shu XO. Dietary B vitamin and methionine intakes and lung cancer risk among female never smokers in China. Cancer Causes Control. 2012 Oct 12.