The link between stress and cancer is not clear-cut.
By Kari Bohlke, ScD
Malignant disease is seen to be but one among many indications of the severe stress upon the nervous system which modern conditions of life involve.…Until society emerges into some calmer sea—or until the conditions under which men and women now commence their voyage are materially improved—a progressive increase in the prevalence of cancer, duly proportionate to the growing severity of the struggle for existence, may be predicted as a matter of course.
Herbert L. Snow, MD, 1890
It was more than 100 years ago that Dr. Herbert Snow, along with several of his colleagues, espoused the belief that psychological stress—“the unmistakable impress of the long endurance of grievously heavy burdens”—made an important contribution to the development of cancer.
Today many cancer survivors share this view. According to one study, more than 60 percent of women with breast or colorectal cancer believe that stress is a cause of their type of cancer. Stress was more frequently mentioned as a cause of cancer than diet, obesity, or lack of exercise.
Can stress really cause cancer? Should we be stressed about stress? The evidence is far from conclusive. Dr. Naja Rod Nielsen, a researcher at Denmark’s National Institute of Public Health and the University of Southern Denmark, has studied the relationship between stress and breast cancer. “In a recent review,” says Dr. Nielsen, “we found no evidence to support a higher risk of developing breast cancer among women with high levels of stress. In some studies we have even found slightly lower risks of developing breast cancer and other hormone-dependent cancers such as endometrial and colorectal cancers among stressed women. A possible explanation may be that stressed women produce less estrogen, which is a major risk factor for hormone-dependent cancers.”
What Is Stress?
The stress response refers to automatic physical changes that occur in response to a real or perceived threat or change. These “threats” can include a wide range of events or situations, such as the death of a spouse, a tight deadline at work, or even positive events such as getting married. It is our perception of these events—and not necessarily the events themselves—that prompts the stress response. An event that causes stress to one individual may not cause stress to another.
In response to a stressful situation, chemical messages are relayed from the brain to the adrenal glands. The adrenal glands, which sit on top of the kidneys, produce the stress hormones cortisol, epinephrine (also known as adrenaline), and norepinephrine (also known as noradrenaline).
These hormones have wide-ranging effects that help us respond to a challenging situation. They sharpen our senses, give us an energy boost, and prepare our muscles for action. In many circumstances these effects are positive and improve our performance. “Several studies have reported that the physiological stress response resulting from acute stress differs markedly from the one resulting from chronic stress,” says Dr. Nielsen. “The physiological effects of acute stressors are in most cases reversible due to the remarkable ability of the human organism to re-establish its balance. In an acute stress situation, the body is prepared to use all of its energy on survival and re-establishment of its balance, which is an appropriate response. The problems mainly arise if the stress response is prolonged and becomes chronic in nature, which may result in permanent disturbances in the balance of vital body systems. I therefore find it most relevant to study chronic exposure to stress in everyday life.”
If the stress response becomes extreme or prolonged, performance—as well as health—can suffer. Stress may influence risk of cardiovascular disease, susceptibility to infections, and other health problems.
Stress and Cancer
Because the effects of stress on the body are wide ranging, it seems plausible that stress could affect our risk of developing cancer or our survival with cancer. In addition to the potential for a direct effect on stress hormones, stress could also have an indirect effect on cancer risk through stress-related behaviors such as smoking or alcohol use.
Stress and the Risk of Developing Cancer
Studies of stress in relation to the risk of developing cancer have produced mixed results. A study conducted in Demark, for example, evaluated the risk of cancer in more than 21,000 parents who had lost a child. The cancer risk in these individuals was compared with the cancer risk in parents who had not lost a child. The study found that mothers who had lost a child had a slightly increased (18 percent higher) risk of developing cancer. The risk was greatest for smoking-related cancers, suggesting that stress-induced behaviors may influence cancer risk.
Similarly, a study conducted among women in the Harvard Nurses’ Health Study evaluated the impact of caregiving and stress on the risk of breast cancer. Women provided information about the number of hours they spent caring for a child or a disabled or ill adult as well as their perceived level of stress. Neither hours spent caregiving nor self-reported stress level were linked with breast cancer risk.
Some studies have even suggested that stress may reduce the risk of developing certain types of cancer. Another study from Denmark followed more than 6,000 women for close to 20 years. Describing stress as sensations of tension, nervousness, impatience, anxiety, or sleeplessness, the researchers asked women about their stress intensity and frequency. Women who reported the highest levels of stress (based on a combined measure of intensity and frequency) at the start of the study were less likely than women who reported the lowest levels of stress to develop endometrial cancer (cancer of the uterine lining) or breast cancer. The reason for this reduced cancer risk is uncertain but could involve stress-induced suppression of estrogen levels.
Not all studies have been so reassuring, however. Research conducted in Sweden found that women who reported the most stress prior to the start of the study were roughly twice as likely to subsequently develop breast cancer as women who reported no stress.
The reasons for the discrepancies among previous studies may involve aspects of study design and uncertainties about how best to define and assess stress. Nevertheless, a recent review of the evidence regarding stress and breast cancer concluded that stress does not appear to be a strong risk factor for breast cancer. The relationship between stress and other types of cancer has received much less attention, but the limited available data do not suggest a major role for stress in cancer development.
Stress and Cancer Survival
A separate issue from whether stress causes cancer is whether stress can influence survival with cancer or risk of cancer recurrence. With respect to breast cancer, Dr. Nielsen explains, “The association between stress and breast cancer relapse has received less attention than the association with breast cancer incidence, and it is still unclear whether stress affects the progression of breast cancer or other cancers. The hypothesis is that stress may render the individual more susceptible to the progression or recurrence of breast cancer either by disturbing recovery or by affecting treatment compliance. Larger studies are needed to address this question.”
The most reliable results are likely to come from large, well-conducted prospective studies. In a prospective study of cancer recurrence, participants are enrolled before recurrence develops. The study participants provide information about the exposure of interest (in this case, stress) and are then followed over time to see who develops a cancer recurrence.
A prospective study of women with newly diagnosed breast cancer found that stressful life events in the year before diagnosis were not related to subsequent risk of breast cancer recurrence and that stressful life events in the years after breast cancer diagnosis were linked with a reduced risk of cancer recurrence. The researchers concluded: “Women with breast cancer need not fear that stressful experiences will precipitate the return of their disease.”
A subsequent study evaluated cancer survival among parents who had or had not lost a child prior to their cancer diagnosis. For all types of cancer combined, parents who had lost a child had a modestly increased (23 percent higher) risk of death. The researchers concluded: “Death of a child is not a strong prognostic factor for cancer survival among parents diagnosed with cancer after the bereavement. However, a small impairment in overall survival cannot be ruled out.”
Based on studies conducted in humans, therefore, it remains uncertain whether stress influences the likelihood of cancer recurrence or survival. Some of this uncertainty stems from a relatively small number of studies that have assessed stress in relation to cancer recurrence, progression, or survival.
What Should We Do?
The current lack of conclusive links between stress and cancer should not encourage us to remain in a stressful job or abandon our yoga classes. There are many reasons other than cancer for managing the stress in our lives. “Let me just emphasize,” states Dr. Nielsen, “that stress cannot be considered a healthy response. Stress is not a desirable state to be in, and it may lead to the development of other diseases, particularly cardiovascular diseases.”
Being aware of the uncertainties surrounding stress and cancer, however, may make us less likely to blame ourselves—and the stress in our lives—when cancer occurs or worsens. In addition, shifting some of our beliefs about stress and cancer may allow us to devote more energy to behaviors that are more likely to influence our cancer risk or cancer prognosis, such as physical activity and maintaining a healthy body weight.
Tips for Stress Management
Although evidence for a link between cancer and stress remains inconclusive, stress management may provide important benefits to cancer survivors, allowing you to derive more pleasure from life; it may also reduce your risk of cardiovascular disease and other health problems.
The National Women’s Health Information Center (www.4women.gov) provides the following tips for managing stress:
- Relax. It’s important to unwind. Each person has her own way to relax. Some ways include deep breathing, yoga, meditation, and massage therapy. If you can’t do these things, take a few minutes to sit, listen to soothing music, or read a book.
- Make time for yourself. It’s important to care of yourself. Think of this as an order from your doctor so you don’t feel guilty! No matter how busy you are, you can set aside at least 15 minutes each day to do something for yourself, like taking a bubble bath, going for a walk, or calling a friend.
- Sleep. Sleeping is a great way to help both your body and your mind. Your stress could get worse if you don’t get enough sleep. You also can’t fight off sickness as well when you sleep poorly. With enough sleep, you can tackle your problems better and lower your risk of illness. Try to get seven to nine hours of sleep every night.
- Eat right. Forgo fast food and instead fuel up with fruits, vegetables, and proteins. Good sources of protein include peanut butter, chicken, and tuna salad. Eat whole grains, such as wheat breads and wheat crackers. Don’t be fooled by the jolt you get from caffeine or sugar. Your energy will wear off.
- Get moving. Physical activity not only relieves tense muscles but also helps your mood too! Your body makes certain chemicals, called endorphins, before and after you work out. They relieve stress and improve your mood.
- Talk to friends. Talking to your friends will help you work through your stress. Friends are good listeners. Finding someone who will let you talk freely about your problems and feelings without judging you does a world of good. It also helps to hear a different point of view. Friends will remind you that you’re not alone.
- Get help from a professional if you need it. Talking to a therapist can help you work through stress and find better ways to deal with problems. For more-serious stress-related disorders such as post-traumatic stress disorder (PTSD), therapy can be helpful. There also are medications that can ease symptoms of depression and anxiety and promote sleep.
- Compromise. Sometimes it’s not worth the stress to argue. Give in once in a while.
- Write down your thoughts. Have you ever typed an e-mail to a friend about your lousy day and felt better afterward? Why not grab a pen and paper and write down what’s going on in your life! Keeping a journal can be a great way to get things off your chest and work through issues. Later you can go back and read through your journal and see how you’ve made progress!
- Help others. Helping someone else can help you. Help your neighbor or volunteer in your community.
- Get a hobby. Find something you enjoy. Be sure to give yourself time to explore your interests.
- Set limits. When it comes to things like work and family, figure out what you can really do. There are only so many hours in a day. Set limits with yourself and others. Don’t be afraid to say no to requests for your time and energy.
- Plan your time. Think ahead about how you’re going to spend your time. Write a to-do list. Figure out what’s most important to do.
- Don’t deal with stress in unhealthy ways. This includes drinking too much alcohol, using drugs, smoking, or overeating.
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