Why dietary supplements increase cancer risk

The current consensus conclusion of the global nutrition community on "dietary supplements may increase the risk of cancer" is only for Excessive dosage, blind indiscriminate supplementation, and wrong supplementation that does not conform to individual metabolic characteristics Three types of situations, not all dietary supplements can cause cancer； The core logic behind the increased risk is that exogenous high-dose nutrient intake disrupts the body's original metabolic balance, immune homeostasis, and cell proliferation control mechanisms.

The most convincing evidence comes from the ATBC cohort study that caused a sensation in the academic world in Finland in 1994: 29,000 long-term smoking male subjects were supplemented with 20 mg of synthetic beta-carotene per day. After 6 years of follow-up, it was found that their incidence of lung cancer was 18% higher than that of the non-supplemented control group, and all-cause mortality also increased by 8%. This result has been quarreling for almost ten years when it first came out. Until now, the two schools of thought have not completely unified their views: One school believes that synthetic beta-carotene is completely different from that found in natural fruits and vegetables. Naturally ingested beta-carotene will act synergistically with flavonoids, dietary fiber and other ingredients to provide an antioxidant effect. A single excessive supplement will turn into a "pro-oxidant" in the high oxidative stress environment of smokers, and instead help free radicals damage cellular DNA. ； The other group believes that the problem lies in the outrageous dosage - 20 mg of beta-carotene is equivalent to eating 20 pounds of carrots in one sitting, which is far beyond the upper limit of the human body's daily metabolism. The excess nutrients will directly interfere with cell apoptosis signals, which is equivalent to "delivering nutrient solution" to mutated cancer cells.

The antioxidant system of the human body is actually like a community football team that has been working together for several years. The vitamins, flavonoids, anthocyanins and other components in fruits and vegetables are players in different positions. There are players who steal the ball and those who are goalkeepers. Only by complementing each other can the "opponent" of free radicals be defended. If you forcefully insert a big-name foreign player (a single high-dose supplement) who is worth over 100 million but doesn't know how to cooperate, the entire formation will be thrown into chaos, which will instead give your opponent an opportunity to take advantage of it. When I was doing community nutrition science popularization in the past two years, I met a 40-year-old sister. There were seven or eight bottles of imported supplements in the drawer, including grape seeds, cranberries, resveratrol, and high-concentration vitamins C and vitamin E. She got up early every day and ate on time more than breakfast. Last year, her physical examination revealed breast nodules of 4a. Fortunately, the biopsy was benign. The doctor asked her to stop all non-essential supplements. Six months later, the nodules were directly reduced to category 2 during a review. Of course, it cannot be directly determined that the nodules are caused by supplements, but a number of large-sample cohort studies have shown that healthy women who have adequate dietary nutrition and long-term supplementation with high-dose vitamin E and synthetic folic acid have a 12%-20% higher risk of breast cancer than those who do not supplement.

It's quite counter-intuitive to say that many people fall into the trap not because they don't know how much to supplement, but because they don't even understand what supplements are suitable for them. Take folic acid, which is a must-have supplement for pregnancy preparation, as an example. The MTHFR gene mutation carrier rate among Chinese people is almost 30%. This group of people has a particularly poor ability to metabolize ordinary synthetic folic acid. If you eat ordinary folic acid without doing genetic screening, unmetabolized folic acid will slowly accumulate in the body, which may increase the risk of colorectal cancer and breast cancer. There are also many girls who love beauty who take whitening pills. Many whitening pills add high doses of cysteine. Long-term excessive consumption will interfere with the melanin metabolism of the skin and increase the risk of melanoma. These are not problems with the supplement itself. It is that the people who take supplements do not consider their own physical conditions at all. They close their eyes and stuff it into their mouths after reading the grass planting post.

Of course, there is no need to kill all supplements with a stick. There are now many studies supporting the view that "reasonable supplementation will not cause cancer": the Chinese Nutrition Society clearly recommends that people with insufficient daily dietary intake should supplement essential nutrients at 1/2 to 1 times the recommended intake. It is completely safe and will not pose the risk of cancer. Appropriate supplementation of vitamin D and calcium for some malnourished elderly people can also reduce the incidence of digestive tract cancer. The reason why people now think that "supplements cause cancer" is that many people regard supplements as a universal health medicine. The nutrients that can be obtained by eating normally must be supplemented by small pills. If you take too much or make the wrong supplements, problems will arise.

I also keep a bottle of B-complex in my drawer. I will take one when I stay up late to catch up on projects, but I never take it every day, let alone stack several supplements at once. To put it bluntly, this thing is to "fill a leak". If you don't eat enough take-out vegetables and fruits, it's absolutely fine to supplement with some vitamin C. But if you eat a pound of vegetables and half a pound of fruits every day, and drink 1000mg of effervescent vitamin C tablets every day, it will simply put a burden on your own metabolism. It will be strange if you don't have problems after a long time.