암 발생 원인 1위 흡연을 위협하는 비만 The disturbing links between too much weight and several types of cancer
The disturbing links between too much weight and several types of cancer
By Laurie McGinley April 14
This image shows pancreatic cancer cells (nuclei in blue) growing as a sphere encased in membranes (red). By growing cancer cells in the lab, researchers can study factors that promote and prevent the formation of deadly tumors. (Min Yu/(Eli and Edythe Broad Center for Regenerative Medicine and Stem Cell Research at USC)/USC Norris Comprehensive Cancer Center/Pancreatic Desmoplasia)
암 발생 원인 1위 흡연 위협하는 '비만' 전문가 "비만 인구 급증에, 30년가까이 감소추세던 암사망 증가 위험" 위, 췌장, 간 등 최소 13종 암 위험도 높여 체중·암 관계규명 위해 내장지방 주목
존스홉킨스대 종양학자 오티스 브롤리는 비만 인구 증가로 인해, 1990년대 초반 이래 감소 추세이던 암 사망이 다시 늘어날 위험도 있다고 이 신문에 말했다. 비만과 과체중은 과거엔 심장 질환과 당뇨병에 관련된 것으로 주로 거론됐으나 최근 여러 연구를 통해 위암, 췌장암, 결장암, 간암, 폐경기 후 유방암 등 최소 13종의 암에 걸릴 위험도를 높이는 것으로 밝혀졌다. 비만한 환자는 또한 정상체중 환자보다 암 재발률이 높고 그에 따라 생존율은 낮다. 하지만, 과도한 체중과 암 사이의 이런 관계에 대해 알고 있는 미국인은 약 절반에 불과하다고 신문은 지적했다. 과잉 체중이 정확히 어떤 기제를 통해 암 발생 위험을 높이는지는 아직 규명되지 않았지만, 연구자들은 장기를 둘러싼 내장 비만에 주목하고 있다. 내장 지방은 단순히 지방 덩어리가 아니라 "대사 활동을 하는 장기"처럼 에스트로겐 같은 호르몬들을 생산하는데, 에스트로겐은 유방암이나 일부 다른 암들의 발생 위험을 높인다고 미국암연구소(AICR)는 보고 있다. 내장 지방은 또 인슐린 수치를 높이는 단백질 분비를 통해 세포 성장을 촉진해 암 가능성을 높일 수도 있다. "신진대사, 염증, 면역력의 복합적인 상호작용을 통해 암 발생에 유리한 환경이 만들어지는 것"이라고 다나-파버암연구소의 유방 종양학자 제니퍼 리지벨은 설명했다. 미국인 10명 중 약 7명은 과체중이거나 비만한 것으로 조사됐다. 지난 수십년간 과체중 성인 비율은 비교적 변함이 없지만, 비만율은 1960년대 초 남성 11%, 여성 16%에서 지난 2015년 조사에 따르면 각각 38%, 41%로 치솟았다. 과체중은 체질량지수(BMI) 25-29, 비만은 30 이상을 말한다. 허친슨센터의 비뇨기과 전문의 조너던 라이트는 "비만도가 높을수록 암 위험이 커지는 것 같다"고 말하고, 과체중과 암 사이에도 연관이 있지만 "비만만큼 강하지는 않다"고 덧붙였다.
Less than one-fifth of subjects in cancer trials are obese/Boston University edited by kcontents 미국국립보건원(NIH)에 따르면, 비만과 가장 강한 관계가 있는 것은 자궁 내막암. 비만이거나 과체중인 여성은 정상 체중에 비해 발병률이 2-4배 높으며, 체중이 늘수록 위험도도 따라 는다. 과체중이거나 비만한 사람은 정상 체중인 사람에 비해 간암과 신장암 위험도도 약 2배 높고, 췌장암은 1.5배 높다. 과체중 여부와 상관없이 뱃살이 나오면 결장 같은 암 위험이 커진다. 이에 따라 체중을 줄이면 암 발생이나 재발 위험도 줄어든다는 가설을 입증하기 위한 연구도 여럿 진행 중이다. 지나친 비만으로 인해 비만 수술을 받은 사람들은 암 발생 위험이 낮아진다는 연구 결과도 있으나, 확증에는 더 많은 연구가 필요하다고 워싱턴 포스트는 말했다. 암 위험도를 줄이기 위해선 체중을 얼마나 줄여야 하는지는 아직 밝혀지지 않았으나 기존 자료들로 보면 5% 감량하면 혈당과 염증에 좋은 영향을 미치는 것으로 나타났다고 다나-파버연구소의 리지벨은 설명했다. 암 위험을 줄이려면 무엇보다 체중 증가를 피해야 하며, 그 핵심은 한끼분 식사량을 줄이고 설탕을 피하며, 야채와 과일, 통곡물, 콩이 많이 든 음식을 먹고, 동물성 단백질 섭취를 줄이는 것이라고 전문가들은 조언한다고 신문은 전했다. [연합뉴스] 매일경제 |
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Smoking has been the No. 1 preventable cause of cancer for decades and still kills more than 500,000 people a year in the United States. But obesity is poised to take the top spot, as Americans’ waistlines continue to expand while tobacco use plummets.
The switch could occur in five or 10 years, said Otis Brawley, a Johns Hopkins oncologist and former chief medical officer of the American Cancer Society. The rise in obesity rates could threaten the steady decline in cancer death rates since the early 1990s, he said.
Yet only about half of Americans are aware of the link between excess weight and cancer. And researchers are struggling to answer such fundamental questions as how surplus weight increases the risk of the disease and whether, conversely, losing weight helps prevent cancer or a recurrence.
Being obese and overweight — long implicated in heart disease and diabetes — has been associated in recent years with an increased risk of getting at least 13 types of cancer, including stomach, pancreatic, colorectal and liver malignancies, as well as postmenopausal breast cancer. Researchers at the American Cancer Society say that excess body weight is linked to about 8 percent of all cancers in the United States and about 7 percent of cancer deaths.
Compared with people of normal weight, obese patients are more likely to see their cancer come back and have a lower likelihood of survival. Perhaps most alarming, young people, who as a group are heavier than their parents, are developing weight-related malignancies, including colorectal cancer, at earlier ages than previous generations, experts say.
'A complex interplay'
Former U.S. Food and Drug Administration Commissioner Dr. David A. Kessler discusses the issue of obesity in America saying. (Washington Post Live)
The precise link between cancer and excess weight isn’t known, but researchers are focusing on the “visceral” fat that surrounds internal organs. Rather than being a harmless glob, this fat is a “metabolically active organ” that produces hormones such as estrogen, which is associated with a higher risk of breast and some other cancers, according to the American Institute for Cancer Research, a nonprofit group that focuses on diet, nutrition and cancer.
The fat also secretes proteins that drive insulin levels higher, which may spur cell growth and increase the possibility of cancer. And it can cause chronic inflammation, another risk factor for the disease, according to the group.
“It’s a complex interplay of metabolism, inflammation and immunity,” said Jennifer Ligibel, a breast oncologist at the Dana-Farber Cancer Institute. “It creates an environment that is more permissive for cancer.”
About 7 in 10 Americans are overweight or obese, according to a 2015 article in JAMA Internal Medicine. People are considered overweight if they have a body mass index (BMI) of 25 to 29, and obese if they have a BMI of 30 or more.
The proportion of adults who are overweight has remained relatively stable in the past several decades, but the obesity rate has soared. In the early 1960s, almost 11 percent of men and nearly 16 percent of women were obese; in 2016, those percentages were 38 percent and 41 percent, respectively, according to the cancer society.
The risk of cancer rises along with excess weight. “It does appear that the risk is greater the more obese you are,” said Jonathan Wright, a urologist at Fred Hutchinson Cancer Research Center in Seattle. There is a link between being overweight and cancer, “but it is not as strong,” he said.
The type of cancer that is most strongly associated with obesity is endometrial, which develops in the lining of the uterus. Obese and overweight women are two to four times as likely to develop the disease as women of normal weight, and the risk rises with increased weight gain, according to the National Institutes of Health.
Meanwhile, people who are overweight or obese are about twice as likely to develop liver and kidney cancer, and about 1.5 times as likely to develop pancreatic cancer than normal-weight people, according to NIH.
In addition, having too much belly fat — a larger waistline — is linked to an increased risk of colorectal and some other cancers, regardless of body weight, the cancer society said.
Several researchers are running clinical trials to try to prove what many already believe — that losing weight reduces the odds of developing cancer or having a recurrence. There are some indications they may be right — severely obese people who have bariatric surgery, for example, lessen their odds of getting cancer — but much more data is needed.
Trials and studies
Carol Massey, who is 59 and was treated for breast cancer two years ago, is enrolled in a nationwide trial designed to see if losing weight makes it less likely breast cancer will come back. She has reduced her calorie intake, stepped up her exercise and gotten regular advice from a health coach based at Boston’s Dana-Farber Cancer Institute, which is leading the Breast Cancer Weight Loss Study, or BWEL.
To be eligible for the trial, women must have a BMI of 27 or higher. The study, which will enroll about 3,100 women, will compare Massey’s group — which gets supervised weight loss and health-education materials — with a group that receives only the educational materials.
Massey, who lives in Paola, Kan., said she quickly came to look forward to her coach’s calls, which initially were once a week. “We got to be friends, she would ask about my family,” she said. “One time, she even called me when she was on vacation in Cabo San Lucas” in Mexico.
Over time, the 5-foot-8 Massey lost 30 pounds. She is now 150 pounds.
Those are the kind of results Ligibel, the principal investigator, is hoping for. If the study shows that slimming down is associated with reduced recurrence, doctors could prescribe a weight-loss program as standard therapy for breast cancer patients — much as cardiac rehabilitation is urged for heart-attack patients. That could pave the way for insurance coverage.
Gail Folloder joined a 16-week program at University of Texas MD Anderson Cancer Center for heavier women at high risk of breast cancer because both of her parents had had cancer and she wanted to prevent it. The 67-year-old Houston resident underwent “hunger training,” which uses continuous glucose monitoring to show participants when they need fuel and urges them to limit their eating to those times.
“The idea is to help people learn to eat only when they are really hungry,” said Karen Basen-Engquist, a behavioral scientist at the cancer center. “We eat for all kinds of reasons — sometimes because we are with other people or because we are bored or stressed.”
It worked for Folloder. “I used to say that I was hungry all the time but I really wasn’t,” she said. “Now I’m more in tune with my body.”
Besides talking to a dietitian weekly, she stepped up her physical activity by using a hula hoop and an exercise bike. Folloder, who is 5-foot-9, went from 219 pounds to 191 pounds.
The women in Folloder’s group will be compared to a “control” group that takes part in a weight-loss program but does not do blood sugar monitoring. Results are expected this year.
Fred Hutchinson’s Wright is focusing on overweight and obese men with low-grade, slow-growing prostate cancer who have decided to take an “active surveillance” approach — which involves monitoring via blood tests, physical exams and biopsies — rather than treatment such as radiation or surgery. He is investigating whether keeping patients’ glucose levels under control through weight loss will prevent the cancer from getting worse and improve survival. The goal is for participants to lose 7 percent of their body weight.
The study is based on the Diabetes Prevention Program, which showed that people at high risk for Type 2 diabetes can prevent or delay the disease by losing a modest amount of weight through dietary changes and increased physical activity.
Nature
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Finding the right diet
Steve Borden, 57, enrolled in the trial, called Prostate Cancer Active Lifestyle or PALS, last November and was assigned to a nutritionist and exercise physiologist to coach him on diet and exercise.
The 5-foot-10 Borden has lost 30 pounds and now weighs 198 pounds. His target is just 1,800 calories a day, and he regularly uses the treadmill and lifts weights. He said a recent test showed his PSA — for prostate-specific antigen, which when elevated can be an indication of cancer — has dropped slightly, although his doctors don’t know whether that is connected to his weight loss.
In general, how much do people need to lose to improve their cancer odds? Ligibel of Dana-Farber said it is not clear but that data suggests a 5 percent reduction in body weight has a beneficial impact on blood sugar and inflammation.
For anyone wanting to reduce their cancer risk, avoiding weight gain in the first place is important, experts say. Brawley of Johns Hopkins said that the goal should be maintaining “energy balance” — consuming no more calories than are burned off through exercise and other activity.
Nutritionists say the key is cutting down on portion sizes, avoiding sugar and aiming for meals that are rich in vegetables, fruits and whole grains and beans and light on animal protein.
Anthony Perre, chief of outpatient medicine at Cancer Treatment Centers of America, said the Mediterranean diet — which emphasizes plant-based food, whole grains and olive oil — has been linked to improved cancer outcomes.
“But the diet that is the right one is the one that you can sustain over the long term,” he said. “Whether it’s Atkins, low-carb or low-calorie, they all work if you stick with them.”
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