Choline is a nutrient the human body requires to operate, yet most people do not consume enough of it. Recently, concerns have emerged regarding a potential relationship between this nutrient and cancer. This article will explore the biological functions of choline, the proposed link to cancer, the scientific evidence, and how to balance intake for overall health.
The Biological Role of Choline
Choline’s importance stems from its versatility in the body’s metabolic processes. It is a component for building the membranes that enclose every cell, ensuring their structural integrity and function. Without sufficient choline, the body cannot produce phosphatidylcholine, a class of phospholipids that constitutes a major part of cellular membranes. This role supports cell signaling, which is how cells communicate with each other to coordinate complex biological activities.
Beyond its structural duties, choline is the direct precursor to acetylcholine, a neurotransmitter that governs memory, mood, and muscle control. The synthesis of acetylcholine is dependent on the availability of choline, making this nutrient a factor in cognitive functions and nervous system regulation. Choline also participates in the transport of fats from the liver, a process that prevents fat accumulation in the organ. Rich dietary sources include animal products like beef liver, eggs, and fish, as well as plant-based options such as soybeans, shiitake mushrooms, potatoes, and cruciferous vegetables.
The Choline-TMAO-Cancer Hypothesis
The concern over choline and cancer centers on a multi-step process that involves the gut microbiome. This proposed mechanism, often called the choline-TMAO-cancer hypothesis, begins with the consumption of choline-rich foods. Certain species of bacteria residing in the human gut can metabolize this dietary choline, producing a compound called trimethylamine (TMA).
Once produced in the gut, TMA is absorbed into the bloodstream and travels to the liver. In the liver, enzymes convert the TMA into a new molecule: trimethylamine N-oxide, or TMAO. It is this final product, TMAO, that is the focus of scientific inquiry regarding cancer risk.
The hypothesis posits that elevated levels of circulating TMAO may contribute to disease by promoting inflammation. Chronic inflammation is a known factor in the development of various diseases, and some research suggests TMAO can activate inflammatory pathways in the body. These pathways can encourage cell proliferation and angiogenesis, the formation of new blood vessels that tumors need to grow.
Examining the Scientific Evidence
Observational studies have explored the connection between choline intake, TMAO levels, and cancer risk, yielding a complex and sometimes contradictory picture. Some research has identified a positive correlation between higher circulating TMAO levels and an increased risk for specific cancers. For example, one study found that higher baseline serum levels of TMAO and choline were associated with a greater risk of distal colorectal cancer. Other analyses have suggested a link between high choline intake and an increased risk of lethal prostate cancer.
Conversely, the scientific literature is not unanimous, and other studies present a different narrative. A meta-analysis of 16 studies found no significant overall association between TMAO levels and cancer incidence. Some research even points to a potentially protective role for choline. A case-control study in China associated higher dietary choline intake with a reduced risk of breast cancer, and animal studies have also suggested that choline deficiency may promote liver cancer.
The source of choline might also be a factor, with some studies suggesting that choline from animal products leads to higher TMAO production than plant-based sources. It is important to remember that these observational studies show correlation, not causation. Many factors, including genetics, diet, and lifestyle, influence both TMAO levels and cancer risk, making it difficult to isolate choline as the sole contributor.
Balancing Choline Intake for Health
Given the evidence, the focus for most individuals should be on maintaining adequate, but not excessive, choline intake as part of a varied diet. The Food and Nutrition Board of the National Academies has established an Adequate Intake (AI) level for choline, which is 550 milligrams per day for adult men and 425 milligrams per day for adult women. These recommendations increase for pregnant and lactating women, who require 450 mg and 550 mg per day, respectively, to support fetal and infant brain development.
Choline deficiency, though rare in healthy individuals, poses clear health risks, including the development of nonalcoholic fatty liver disease (NAFLD) and muscle damage. Symptoms of deficiency can include fatigue, memory problems, and muscle aches. The body can produce a small amount of choline on its own, but it is not enough to meet the body’s needs, making dietary intake necessary.
For most people, obtaining choline from a balanced diet that includes a mix of animal and plant-based foods is a sound strategy. The potential risks associated with TMAO appear more pronounced with very high intakes of certain foods, rather than from the moderate consumption of choline-containing foods as part of a healthy dietary pattern.