Study: Drinking coffee or tea may improve survival after breast cancer

IN-DEPTH REVIEW OF RESEARCH

Study background

Coffee and tea are some of the most commonly consumed beverages worldwide. Both contain many active ingredients, including caffeine, which is the most well-known active ingredient. Coffee, tea and caffeine have been linked to improved insulin sensitivity, reduced inflammation and antioxidant activity. Each of these factors has been suggested to improve cancer prevention.

Coffee has been implicated in protection against liver and endometrial cancer, however, the effect of coffee or tea on breast cancer has not been clear. Previous findings regarding these beverages and breast cancer outcomes have been contradictory. In several studies, drinking coffee before a diagnosis of breast cancer was not linked to more or less cancer-specific deaths or deaths from any cause. On the other hand, in the Cancer Prevention Study II, the level of coffee consumption before a breast cancer diagnosis was linked to lower breast cancer death in nonsmokers.

In studies of coffee consumption after a breast cancer diagnosis, one small, 96-person study saw an increased risk of breast cancer death, while another larger 576-person study saw a decrease in breast cancer mortality but only among those who were treated with tamoxifen for estrogen receptor-positive cancer.

In this study, researchers look at the association between coffee and tea consumption and breast cancer in two large groups of women: participants in the Nurses' Health Study and the Nurses' Health Study II. Participants in these studies reported beverage consumption along with many other dietary and health factors both before and after their breast cancer diagnoses.

Researchers of this study wanted to know

Researchers wanted to know whether coffee or tea consumption affects the chance of death due to breast cancer or to any other cause. 

Populations looked at in this study

This study looked at information from 8,900 participants with breast cancer (stages 1 to 3) from the Nurses’ Health Study (NHS) and the Nurses’ Health Study II (NHSII). Participants were excluded if their diet information was missing at the time of the survey 12 months after diagnosis, their total energy intake was unusually low or high (below 600 or above 3,500 kcal/day), more than 70 food items or all coffee and tea questions were left blank on the food frequency questionnaire (FFQ), they had been diagnosed with any cancer other than non-melanoma skin cancer prior to their breast cancer diagnosis or they were diagnosed initially diagnosed with stage 4 cancer.

Study design

Researchers looked at coffee and tea consumption using a validated food frequency questionnaire (FFQ) given before participation and every four years after breast cancer diagnosis for up to 30 years (the average follow-up time was 11.5 years). Coffee or tea consumption was separated into regular or decaffeinated groups and then broken down by the average amount consumed per day: more than three cups, two to three cups, 0 to two cups or none.

Participants self-reported breast cancer diagnoses on health questionnaires every two years. Cancer diagnosis and type, stage and treatment were confirmed by medical records and pathology reports. In some cases, tissue samples were used to determine the presence or absence of tumor biomarkers. Death reports were confirmed by death certificates and medical record reviews by physicians to determine the cause of death. Participants were followed after returning their first FFQ before a breast cancer diagnosis through the end of the study (June 1, 2014, for NHS and June 2, 2015, for NHSII) or death.

Study findings

Exactly 8,900 women participated in this study. During the follow-up time (an average of 11.5 years), 1,054 participants died of breast cancer and 2,501 died of any cause (including breast cancer). Participants drank 1.7 cups of coffee and 0.7 cups of tea on average after their breast cancer diagnosis.

Drinking more coffee is linked to a lower chance of dying of breast cancer

Participants who drank greater amounts of coffee after a breast cancer diagnosis had a lower risk of dying of breast cancer less often than participants who did not drink coffee.

• Those who drank more than three cups of coffee each day had a 25% lower risk of dying of breast cancer than those who drank no coffee.
• For each daily cup of caffeinated coffee, the risk of breast cancer death was 7% lower; each cup of decaffeinated coffee reduced risk by 2%.

Participants who drank more coffee had a lower risk of dying from any cause than those who did not drink coffee.

• Those who drank more than 2 to 3 cups of coffee daily had a 24% lower risk of dying of any cause than those who drank no coffee.
• Those who drank more than 3 cups of coffee daily had a 26% lower risk of dying of any cause than those who drank no coffee.
• For each cup of caffeinated coffee per day, the risk of death from any cause was 7% lower; the risk was 5% lower for each cup of decaffeinated coffee.

Drinking tea and risk of dying of breast cancer

Participants who drank more tea had a lower risk of dying from any cause, but not specifically of breast cancer than those who did not drink tea.

• Those who drank more than 3 cups of tea each day had a 26% lower risk of dying of any cause than those who drank no tea.
• Women with drank more tea were also more likely to have chemotherapy or hormonal treatment.

Overall caffeine consumption and breast cancer death

When researchers looked at caffeine intake from all sources, greater caffeine intake was linked to fewer breast cancer-specific deaths and fewer deaths from any cause. Overall, caffeine consumed after breast cancer diagnosis seemed to be protective.

Type of cancer and coffee or tea consumption

To look at cancer types, researchers grouped consumption of caffeinated and decaffeinated coffee and grouped consumption of caffeinated and decaffeinated tea. They considered whether the risk of breast cancer death was different between groups that consumed more versus less coffee or tea in different types of breast cancer.

Greater coffee consumption was related to better survival of participants whose cancer had certain tumor markers:

• ER-positive breast cancer
• ER-negative breast cancer
• IR-negative breast cancer
  • These cancers lack a type of Insulin growth factor-receptor called IR.
• Luminal A breast cancer
  • These cancers are estrogen receptor-positive, progesterone receptor-positive and HER2-negative with low levels of the protein Ki-67.
• Luminal B breast cancer
  • ER-receptor positive, PR-receptor positive and HER-negative with high levels of the protein Ki-67 or HER2-positive.

Breast cancer survival was not greater among participants who were high consumers of coffee and had IR-positive breast cancer or those with HER2-enriched (estrogen-receptor positive, progesterone-receptor positive, HER2-positive) or basal-like/triple-negative (estrogen receptor-negative, progesterone receptor-negative, HER2-negative) breast cancers. Not all tumors are tested for all of these markers.

Lack of impact of coffee consumption before breast cancer diagnosis

Coffee and tea consumption before breast cancer diagnosis was not linked to breast cancer-specific deaths or all-cause deaths. Whether participants drank lots of coffee before their breast cancer diagnosis did not increase or decrease their risk of breast cancer-related death (or all-cause death). Rather, coffee consumption after breast cancer diagnosis accounted for decreased risk of breast cancer deaths.

However, findings were different for participants who drank more coffee before their breast cancer diagnosis and then drank less coffee after diagnosis.

Decreasing coffee consumption after breast cancer diagnosis increased risk

Participants who drank more than two cups of coffee before cancer diagnosis and then drank no coffee after a breast cancer diagnosis had a 91% higher risk of death from breast cancer than participants who did not drink coffee before or after a breast cancer diagnosis.

Participants who drank more than two cups of coffee before cancer diagnosis and then drank less (0 to 2 cups of coffee each day) after breast cancer diagnosis had a 34% higher risk of death from breast cancer than participants who did not drink coffee before or after a breast cancer diagnosis.

Researchers cannot explain why this change in coffee consumption increased risk. Nor could they distinguish this from other possible factors that are varying in the same way.

Other factors may influence the risk of breast cancer death among coffee drinkers

Human research is complicated because researchers cannot always vary a specific aspect of a person's life or diet. Several things that vary at the same time are called confounding factors; it can be difficult to tell which factor is responsible for a particular effect on health.

In the case of coffee consumption and breast cancer deaths, researchers noted several confounding factors that with potential impacts that could not be separated. Participants with higher coffee consumption after diagnosis were more likely to:

• drink alcohol
• smoke
• consume more animal fat
• used aspirin more frequently after diagnosis

and less likely to:

• have radiotherapy
• have chemotherapy.

While researchers tried to account for the effect of these confounding factors, the effect they attribute to coffee or tea consumption may be in part because of these confounding factors.

Researchers noted that several factors did not contribute to the effects observed, including:

• age
• body mass index (BMI) after breast cancer diagnosis
• stage of cancer
• amount of coffee or tea consumed on average before breast cancer diagnosis

Strengths and Limitations

Overall, this was a well-designed and appropriately analyzed study. The researchers were careful to point out weaknesses of their interpretation as well as highlight major findings.

Strengths

• A major strength of this study is that 8,900 participants were enrolled. Larger studies are typically more accurate because there is a greater chance of detecting differences when they occur.
• Another strength is the regular follow-up on participants’ health. Researchers followed the health history and food and drink consumption history of participants every 4 years throughout the study rather than by asking participants to recall memories of health and diet history. This type of prospective study (looking forward in time) is considered better than a retrospective study (looking back in time) because the researchers have greater confidence that the results are accurate.
• The time of follow-up was long (11.5 years on average) allowing researchers to have a comprehensive understanding of the coffee and tea consumption of the participants.
• Self-reports of health and breast cancer diagnosis were validated with reviews of medical records and where needed, testing tumor tissue to verify cancer type.

Limitations

• The biggest limitations of this study are confounding factors. Several factors (smoking, alcohol consumption, less use of chemotherapy and radiation therapy) vary in the same way that coffee and tea consumption do; if a person drank more coffee they also usually smoked more and drank more alcohol. While the researchers used statistical tools to ask whether these factors rather than coffee were responsible for the findings, concern remains that the decrease in the risk of breast cancer deaths may be from a combination of these factors in addition to coffee or tea consumption.
• The study population was not diverse. The majority of participants were well-educated, non-Hispanic white women. These findings may not be generalizable to the more diverse U.S. population.
   

Context

A few smaller studies have also looked at coffee consumption after a breast cancer diagnosis. The findings in this study are similar to a prior study of 576 women with ER-positive cancer who were treated with tamoxifen, drank two or more cups of coffee a day and had improved survival. However, some previous research conflicts these conclusions: a study of 96 women saw worse survival with more coffee consumption.

Like this study, prior studies looking at coffee consumption before breast cancer diagnosis similarly saw no link to survival apart from one report of improved survival among nonsmokers with high coffee consumption.

Overall, this study builds on our knowledge about the impact of coffee and tea consumption on breast cancer.

Conclusions

High coffee consumption is linked to improved breast cancer-specific survival and overall survival. High tea consumption is linked to improved overall survival. Both decaffeinated and caffeinated beverages contribute to the improved survival observed. Breast cancer survivors may benefit from regularly drinking tea or coffee.

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posted 8/31/21