"Fat women who refuse to diet 'are more likely to
get cancer'," states the Mail Online, using a headline that is both
inaccurate and offensive.The study it reports on looked at the relationship
between weight during adulthood, and cancer risk.
The researchers found that duration of time spent
overweight or obese,
as well as the degree, seems to have a compounding effect on cancer risk. But
they did not look at whether the women in the study were asked to lose weight
by dieting.
Cancers linked to obesity include breast, bowel and womb cancer
This latest study of more than 70,000 women took
multiple measurements over about 12 years and also used women's own estimates
of their weight at ages 18, 35 and 50, to calculate how many years they
had been overweight or obese. They then calculated the risk of getting an
obesity-related cancer, linked to decades of being overweight or obese.
They found that each decade of overweight was linked
to a 7% increased risk of obesity-related cancer. Womb cancer
(specifically endometrial cancer; a cancer of the lining of the womb) was most
strongly linked to obesity. Both duration and degree of overweight increased
cancer risk.
The study has limitations, but suggests that keeping
to a healthy weight throughout life may help women to avoid some cancers.
If you are concerned about your weight then try the NHS
weight loss plan. This is a 12 week plan designed to help people
lose weight in a sustainable way through a combination of healthy eating and
exercise
What did the research involve?
Researchers looked at information from a big group of
postmenopausal women without cancer, taking part in a long-term cohort study in
the US, called the Women's Health Initiative.
They calculated how long they had been either normal
weight, overweight or obese, and followed them to see how many of them got one
of 10 cancers thought to be linked to weight, over a 12-year period.
Weight was assessed with the widely used body mass
index (BMI) measurement, where:
• 18.5 to 24.9 means you're a healthy weight
• 25 to 29.9 means you're overweight
• 30 to 39.9 means you're obese
• 40 or above means you're severely obese
After adjustment to take account of confounding
factors that could affect cancer risk, including age, smoking,
physical exercise, diet and whether women took hormone replacement therapy
(HRT), they calculated risks of cancers per decade of overweight or obesity.
The researchers used measurements of weight and height
taken during the study, and asked the women to remember their measurements at
ages 18, 35 and 50. Using this information, they calculated how long the women
had been normal weight, overweight or obese during their adult lives. The
cancers monitored were:
• breast cancer (postmenopausal)
• colon cancer
• endometrial (womb) cancer
• gallbladder cancer
• liver cancer
• ovarian cancer
• pancreatic cancer
• rectal cancer
• renal (kidney) cancer
• thyroid cancer
They also calculated the effect of different degrees
of overweight, by looking at the number of units of BMI over the healthy limit
of 25 units that women were, for each time period.
This allowed them to compare both time and level
of overweight.
What were the basic results?
There were 6,301 cancers among the 73,913 women in the
study, over 12 years. About two thirds of women were overweight or obese at
some point during adulthood. On average, overweight women were overweight for
31 years of their adult lives.
For every 10 years of being overweight, women had a 7%
higher chance of being diagnosed with one of the cancers (hazard ratio
(HR) 1.07, 95% confidence
interval (CI) 1.06 to 1.09). The risk was increased for colon and
postmenopausal breast cancers but highest for endometrial cancer and kidney
cancer. No link was seen between time spent overweight and rectal, liver,
gallbladder, pancreatic, ovarian or thyroid cancer.
When researchers took into account the degree of
overweight, the link became stronger, especially for endometrial cancer. Each
additional decade spent with a BMI of 35 (10 units of BMI over normal weight)
carried a 37% increase in the risk of endometrial cancer (HR 1.37, 95% CI 1.29
to 1.46).
How did the researchers interpret the results?
The researchers said they cannot show that time spent
overweight causes cancer, but that their findings "suggest that reducing
overweight duration in adulthood could reduce cancer risk and that obesity
prevention is important from the outset". They said this meant that
healthcare services should recognise that "excess body weight in women is
important to manage, regardless of the age of the patient."
Conclusion
This study adds to evidence that being overweight or
obese for long periods of time may increase the risk of certain cancers, just
as it increases the risk of cardiovascular disease and diabetes.
The study's size and use of BMI measurements over time
mean it is likely to be more reliable than smaller studies, or those that look
at BMI only at one time point. The design allows researchers to look at how
weight during a lifetime, rather than at one single point in life, may affect
cancer risk.
However, there are limitations. It's an observational
study, so while researchers took account of known confounding factors such as
smoking and exercise, it's always possible some factors were not accounted for.
This means the study cannot prove that overweight directly caused cancer. The
other main concern is that it relied on women remembering and correctly
reporting their weight decades earlier, at ages 18 and 35.
These caveats aside, the study is a serious attempt to
quantify the risk that overweight and obesity contribute to cancer risk.
Obesity levels have been rising in recent decades and figures from Public
Health England show 65% of men and 58% of women in England were overweight or
obese in 2014.
The best way to keep to a healthy weight throughout
life is to eat a healthy, balanced diet and take plenty of exercise. Some
people struggle with their weight more than others, and it can be hard to shift
weight once you've put it on.
If you're worried about your weight and want
help in reaching a healthy weight, you can talk to your GP for advice or see our
information on healthy weight loss.
Source: http://www.nhs.uk/news/2016/08August/Pages/Longer-a-woman-is-overweight-the-higher-her-cancer-risk-may-be.aspx
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