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Our assessments of evidence for each medical benefit fall into one of these categories:

• Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
• Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
• Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
• Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
• Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
• Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

Learn more about how we research and rate therapies and practices in How We Rate Therapies ›

• Slightly to modestly lower mortality among people with cancer with greater perceived social support, larger social networks, or a spouse compared with other people in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 87 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹Pinquart M, Duberstein PR. Associations of social networks with cancer mortality: a meta-analysis. Critical Reviews in Oncology/Hematology. 2010 Aug;75(2):122-37.
• Lower cancer survival among men with few social connections compared to others in a large observational study²Reynolds P, Kaplan GA. Social connections and risk for cancer: prospective evidence from the Alameda County Study. Behavioral Medicine. 1990 Fall;16(3):101-10.
• 2-year longer lifespan across 20 years of follow up among middle-aged men who developed cancer and were married or living with a partner at the start of the study, compared to those who were single, divorced, or widowed in a large observational study³Kraav S, Lehto SM, Kauhanen J, Hantunen S, Tolmunen T. Loneliness and social isolation increase cancer incidence in a cohort of Finnish middle-aged men. A longitudinal study. Psychiatry Research. 2021 May;299:113868.
• Slightly lower incidence of suicidal thoughts (suicidal ideation) among people with cancer with higher levels of social support compared to lower levels in a meta-analysis of 12 observational studies⁴Du L, Shi HY et al. Association between social support and suicidal ideation in patients with cancer: a systematic review and meta-analysis. European Journal of Cancer Care (Engl). 2021 Mar;30(2):e13382.

Good evidence of better survival among people with breast cancer with higher levels of social support

• Better breast cancer prognosis among people with breast cancer reporting social support or marriage compared to other people in a systematic review of 8 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵Falagas ME, Zarkadoulia EA et al. The effect of psychosocial factors on breast cancer outcome: a systematic review. Breast Cancer Research. 2007;9(4):R44.
• Lower survival among women with breast cancer with high levels of both social pain (determined by social network size, social support, loneliness, and social well-being) and physical pain compared to women with low levels of both types of pain in a large observational study⁶Kroenke CH, Alexeeff S, Kushi LH, Kwan ML, Matthews KA. Clustering of social and physical pain variables and their association with mortality in two population-based cohorts. Psychosomatic Medicine. 2021 Apr 1;83(3):228-238.
• Double the risk of cancer-specific mortality and 66% higher overall mortality among women with breast cancer who were socially isolated before diagnosis compared with women who were socially integrated, although being married had no effect, in a large observational study⁷Kroenke CH, Kubzansky LD, Schernhammer ES, Holmes MD, Kawachi I. Social networks, social support, and survival after breast cancer diagnosis. Journal of Clinical Oncology. 2006 Mar 1;24(7):1105-11.
• Better 7-year survival among people newly diagnosed with breast cancer with surgically treated localized or regional disease who used 1 or more confidants in the 3 months after surgery compared to those who used no confidants in a mid-sized observational study⁸Maunsell E, Brisson J, Deschênes L. Social support and survival among women with breast cancer. Cancer. 1995 Aug 15;76(4):631-7.
• 64% higher breast cancer-specific mortality and 69% higher overall mortality among socially isolated women compared to socially integrated women in a mid-sized observational study⁹Kroenke CH, Michael YL et al. Postdiagnosis social networks and breast cancer mortality in the After Breast Cancer Pooling Project. Cancer. 2017 Apr 1;123(7):1228-1237/

Treatment adherence: good evidence of greater adherence to breast cancer treatment with higher levels of social support

• Higher adherence to use of oral anticancer medications among women with breast cancer with more social support or with stronger patient-provider relationships compared to other women in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 21 observational studies¹⁰Lin C, Clark R, Tu P, Bosworth HB, Zullig LL. Breast cancer oral anti-cancer medication adherence: a systematic review of psychosocial motivators and barriers. Breast Cancer Research and Treatment. 2017 Sep;165(2):247-260.
• Higher treatment adherence 4 months after prescription for adjuvant endocrine therapy among people with breast cancer with higher levels of social support compared to lower levels in a mid-sized observational study¹¹Bright EE, Stanton AL. Prospective investigation of social support, coping, and depressive symptoms: a model of adherence to endocrine therapy among women with breast cancer. Journal of Consulting and Clinical Psychology. 2018 Mar;86(3):242-253.

• 13% lower mortality among women with ovarian cancer with social support reflecting connection to others (social attachment) compared to other women in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹²Lutgendorf SK, De Geest K et al. Social influences on clinical outcomes of patients with ovarian cancer. Journal of Clinical Oncology. 2012 Aug 10;30(23):2885-90.

• Higher likelihood of more advanced cancer at diagnosis and 40% higher risk of cancer-specific mortality among single men (unmarried, widowed, divorced, or separated) with prostate cancer compared to married men in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹³Tyson MD, Andrews PE et al. Marital status and prostate cancer outcomes. Canadian Journal of Urology. 2013 Apr;20(2):6702-6.

• Lower PSA levels after one year among men with early-stage prostate cancer not receiving conventional treatment at recruitment and participating in a lifestyle intervention including a health-promoting diet, physical activity, group support, and stress management compared to usual care in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁴Ornish D, Weidner G et al. Intensive lifestyle changes may affect the progression of prostate cancer. Journal of Urology. 2005 Sep;174(3):1065-9.

• Higher incidence of a large waist-to-hip ratio among middle-aged women with lower levels of perceived social support compared to other women in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁵Wing RR, Matthews KA, Kuller LH, Meilahn EN, Plantinga P. Waist to hip ratio in middle-aged women. Associations with behavioral and psychosocial factors and with changes in cardiovascular risk factors. Arteriosclerosis and Thrombosis. 1991 Sep-Oct;11(5):1250-7.

• Higher markers of immune activation among people with ovarian cancer with social support compared to those without social support in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁶Lutgendorf SK, Sood AK et al. Social support, psychological distress, and natural killer cell activity in ovarian cancer. Journal of Clinical Oncology. 2005 Oct 1;23(28):7105-13.
• A lower marker of immune activation (natural killer cell (NK) activity), which relates to worse prognosis, among women with breast cancer with higher fatigue or depression and lower social support in a small observational study¹⁷Levy SR, Herberman ML et al. Correlation of stress factors with sustained depression of natural killer cell activity and predicted prognosis in patients with breast cancer. Journal of Clinical Oncology. 1987 Mar;5(3):348-53.

• Lower levels of vascular endothelial growth factor (VEGF)—released by cells to create a blood supply, and necessary to enable tumor growth— before surgery among people with ovarian cancer with higher levels of social well-being compared to lower levels in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁸Lutgendorf SK, Johnsen EL et al. Vascular endothelial growth factor and social support in patients with ovarian carcinoma. Cancer. 2002 Aug 15;95(4):808-15.
• Stronger expression of VEGF among people with colorectal tumors experiencing loneliness compared to other people in a small observational study¹⁹Nausheen B, Carr NJ et al. Relationship between loneliness and proangiogenic cytokines in newly diagnosed tumors of colon and rectum. Psychosomatic Medicine. 2010 Nov;72(9):912-6.

• Higher risk of more severe side effects of cancer treatment among unmarried or single (without a partner) people with colorectal cancer compared to partnered people in a systematic review of 4 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies²⁰Han CJ, Yang GS, Syrjala K. Symptom experiences in colorectal cancer survivors after cancer treatments: a systematic review and meta-analysis. Cancer Nursing. 2020 May/Jun;43(3):E132-E158.

• Less anxiety 1 year after surgery among people with colorectal cancer who had more social support compared to those with less social support in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²¹Gonzalez-Saenz de Tejada M, Bilbao A et al. Association between social support, functional status, and change in health-related quality of life and changes in anxiety and depression in colorectal cancer patients. Psycho-Oncology. 2017 Sep;26(9):1263-1269.
• Lower rates of anxiety during treatment among people with lung cancer reporting higher levels of family support compared to other people in a mid-sized observational study²²Lekka D, Pachi A et al. Pain and anxiety versus sense of family support in lung cancer patients. Pain Research and Treatment. 2014;2014:312941.

• Lower depressive symptoms 1 month after receiving a first prescription for adjuvant endocrine therapy among people with breast cancer with higher levels of social support compared to lower levels in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²³Bright EE, Stanton AL. Prospective investigation of social support, coping, and depressive symptoms: a model of adherence to endocrine therapy among women with breast cancer. Journal of Consulting and Clinical Psychology. 2018 Mar;86(3):242-253.
• Better mood with spouse support and worse mood with spouse criticism among people with cancer in a mid-sized observational study²⁴Manne SL, Pape SJ, Taylor KL, Dougherty J. Spouse support, coping, and mood among individuals with cancer. Annals of Behavioral Medicine. 1999 Spring;21(2):111-21.
• Less depression 1 year after surgery among people with colorectal cancer who had more social support compared to those with less social support in a mid-sized observational study²⁵Gonzalez-Saenz de Tejada M, Bilbao A et al. Association between social support, functional status, and change in health-related quality of life and changes in anxiety and depression in colorectal cancer patients. Psycho-Oncology. 2017 Sep;26(9):1263-1269.
• Higher levels of concurrent pain, depression, and fatigue among people with cancer experiencing loneliness compared to others in 2 mid-sized observational studies²⁶Jaremka LM, Andridge RR et al. Pain, depression, and fatigue: loneliness as a longitudinal risk factor. Health Psychology. 2014 Sep;33(9):948-57; Jaremka LM, Fagundes CP et al. Loneliness predicts pain, depression, and fatigue: understanding the role of immune dysregulation. Psychoneuroendocrinology. 2013 Aug;38(8):1310-7.
• Lower incidence of hopelessness among people with breast cancer with higher perceived social support compared to those with higher perceived support in a small observational study²⁷Öztunç G, Yeşil P, Paydaş S, Erdoğan S. Social support and hopelessness in patients with breast cancer. Asian Pacific Journal of Cancer Prevention. 2013;14(1):571-8.
• Less mood disturbance among people with metastatic and/or recurrent breast cancer with more people in their support system compared to fewer people, but only among people who had undergone greater life stress, in a mid-sized observational study²⁸Koopman C, Hermanson K, Diamond S, Angell K, Spiegel D. Social support, life stress, pain and emotional adjustment to advanced breast cancer. Psycho-Oncology. 1998 Mar-Apr;7(2):101-11.
• Higher total mood disturbance among people with metastatic and/or recurrent breast cancer with more aversive social contact compared to less aversive social contact, and especially among people who had undergone greater life stress, in a mid-sized observational study²⁹Koopman C, Hermanson K, Diamond S, Angell K, Spiegel D. Social support, life stress, pain and emotional adjustment to advanced breast cancer. Psycho-Oncology. 1998 Mar-Apr;7(2):101-11.

• Higher levels of concurrent pain, depression, and fatigue among people with cancer experiencing loneliness compared to other people in 2 mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies³⁰Jaremka LM, Andridge RR et al. Pain, depression, and fatigue: loneliness as a longitudinal risk factor. Health Psychology. 2014 Sep;33(9):948-57; Jaremka LM, Fagundes CP et al. Loneliness predicts pain, depression, and fatigue: understanding the role of immune dysregulation. Psychoneuroendocrinology. 2013 Aug;38(8):1310-7.

• Higher levels of concurrent pain, depression, and fatigue among people with cancer experiencing loneliness compared to other people in 2 mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies³¹Jaremka LM, Andridge RR et al. Pain, depression, and fatigue: loneliness as a longitudinal risk factor. Health Psychology. 2014 Sep;33(9):948-57; Jaremka LM, Fagundes CP et al. Loneliness predicts pain, depression, and fatigue: understanding the role of immune dysregulation. Psychoneuroendocrinology. 2013 Aug;38(8):1310-7.
• Higher levels of pain are linked to decreased levels of social activities and social support in 7 of 8 studies in a review.³²Zaza C, Baine N. Cancer pain and psychosocial factors: a critical review of the literature. Journal of Pain and Symptom Management. 2002 Nov;24(5):526-42.

• Better reported mental health and ability to cope with the psychosocial impacts of treatments among women with breast cancer with emotional and practical support from family and friends compared to those with less support in a meta-synthesis of 28 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies³³Rajagopal L, Liamputtong P, McBride KA. The lived experience of Australian women living with breast cancer: a meta-synthesis. Asian Pacific Journal of Cancer Prevention. 2019 Nov 1;20(11):3233-3249.
• Poorer psychological outcomes (anxiety, depression and distress) among people with testicular cancer with inadequate coping resources, including lack of social support, compared to other people in a systematic review of 36 observational studies of generally fair to good quality³⁴Smith AB, Rutherford C et al. A systematic review of quantitative observational studies investigating psychological distress in testicular cancer survivors. Psycho-Oncology. 2017 Nov 23.
• Better emotional well-being 2 years after diagnosis among men with localized prostate cancer receiving either radical prostatectomy or radiotherapy who had higher levels of social support compared to those with less support in a mid-sized observational study³⁵Zhou ES, Penedo FJ et al. Longitudinal effects of social support and adaptive coping on the emotional well-being of survivors of localized prostate cancer. The Journal of Supportive Oncology. 2010;8(5):196-201.
• Lower likelihood of feelings of loneliness among people with cancer with social support compared to other people in a small observational study³⁶Adams RN, Mosher CE et al. Cognitive and situational precipitants of loneliness among patients with cancer: a qualitative analysis. Oncology Nursing Forum. 2016 Mar;43(2):156-63.

• Better reported physical health among women with breast cancer having a supportive relationship with a spouse compared to other women in a meta-synthesis of 28 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies³⁷Rajagopal L, Liamputtong P, McBride KA. The lived experience of Australian women living with breast cancer: a meta-synthesis. Asian Pacific Journal of Cancer Prevention. 2019 Nov 1;20(11):3233-3249.
• Less impact of depressive symptoms on quality of life among people with breast cancer with greater social support compared to other people in a mid-sized observational study³⁸Huang CY, Hsu MC. Social support as a moderator between depressive symptoms and quality of life outcomes of breast cancer survivors. European Journal of Oncology Nursing. 2013 Dec;17(6):767-74.
• Better quality of life among people with advanced cancer who perceived they had high levels of social support compared to other people in a mid-sized observational study³⁹Applebaum AJ, Stein EM et al. Optimism, social support, and mental health outcomes in patients with advanced cancer. Psycho-oncology. 2014;23(3):299-306.
• Better quality of life among people with cancer with emotional support primarily from small, dense networks of mostly family members compared to those with less support in a mid-sized observational study⁴⁰Courtens AM, Stevens FC, Crebolder HF, Philipsen H. Longitudinal study on quality of life and social support in cancer patients. Cancer Nursing. 1996 Jun;19(3):162-9.
• Higher subjective well-being among women recently completing breast cancer treatment who had higher levels of social support compared to other women in a mid-sized observational study⁴¹McDonough MH, Sabiston CM, Wrosch C. Predicting changes in posttraumatic growth and subjective well-being among breast cancer survivors: the role of social support and stress. Psycho-Oncology. 2014 Jan;23(1):114-20.

• Higher risk of distress among people with breast cancer with lower social support or being unmarried compared to other people in a systematic review of 42 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁴²Syrowatka A, Motulsky A et al. Predictors of distress in female breast cancer survivors: a systematic review. Breast Cancer Research and Treatment. 2017;165(2):229-245.
• Fewer posttraumatic stress symptoms and higher posttraumatic growth among adults with cancer with social support compared to other people in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 5 observational studies⁴³Shand LK, Cowlishaw S, Brooker JE, Burney S, Ricciardelli LA. Correlates of post-traumatic stress symptoms and growth in cancer patients: a systematic review and meta-analysis. Psychooncology. 2015 Jun;24(6):624-34.
• Higher posttraumatic growth among women recently completing breast cancer treatment who had higher levels of social support compared to lower levels in a mid-sized observational study⁴⁴McDonough MH, Sabiston CM, Wrosch C. Predicting changes in posttraumatic growth and subjective well-being among breast cancer survivors: the role of social support and stress. Psycho-Oncology. 2014 Jan;23(1):114-20.

• Higher risk of depression onset or relapse among people without social support compared to others in a review of observational studies⁴⁵Paykel ES. Life events, social support and depression. Acta Psychiatrica Scandinavica. Supplementum. 1994;377:50-8.
• Less depression among people with impaired activities of daily living receiving clinical management but no antidepressant medication and also receiving greater perceived social support compared to those with less social support in a mid-sized controlled trial⁴⁶Oxman TE, Hull JG. Social support and treatment response in older depressed primary care patients. Journals of Gerontology Series B. Psychological Sciences and Social Sciences. 2001 Jan;56(1):P35-45.

• Higher cancer mortality among people without cancer at baseline who were divorced compared to married people, with higher mortality risk for men (28% higher if divorced compared to married) than women (16% higher risk if divorced), and slightly higher risk if widowed, but no difference in risk between married and never-married people, in a very large meta-analysis of 6 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁴⁷Wang Y, Jiao Y et al. Sex differences in the association between marital status and the risk of cardiovascular, cancer, and all-cause mortality: a systematic review and meta-analysis of 7,881,040 individuals. Global Health Research and Policy. 2020 Feb 28;5:4.
• Higher cancer mortality among people without cancer at baseline over about 20 years among the most isolated people compared to the least isolated, but only among white people and not black Americans in a very large observational study⁴⁸Alcaraz KI, Eddens KS et al. Social isolation and mortality in US Black and White men and women. American Journal of Epidemiology. 2019 Jan 1;188(1):102-109.
• Greater risk of cancer among middle-aged men experiencing loneliness compared to others in a large 30-year observational study⁴⁹Kraav S, Lehto SM, Kauhanen J, Hantunen S, Tolmunen T. Loneliness and social isolation increase cancer incidence in a cohort of Finnish middle-aged men. A longitudinal study. Psychiatry Research. 2021 May;299:113868.
• Higher cancer mortality among socially isolated women without cancer at baseline compared to others in a large observational study⁵⁰Reynolds P, Kaplan GA. Social connections and risk for cancer: prospective evidence from the Alameda County Study. Behavioral Medicine. 1990 Fall;16(3):101-10.

• No evidence of an effect on risk of breast cancer among women experiencing widowhood or divorce compared to other women in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 8 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵¹Santos MC, Horta BL, Amaral JJ et al. Association between stress and breast cancer in women: a meta-analysis. Cadenos de Saude Publica. 2009;25 Suppl 3:S453-63.
• Increased risk of breast cancer among women with inadequate social support compared to other women in a mid-sized observational study⁵²Yıldırım NK, Özkan M et al. Possible role of stress, coping strategies, and life style in the development of breast cancer. International Journal of Psychiatry Medicine. 2018 May;53(3):207-220.

• 48% higher incidence of colorectal cancer and more than 3 times the risk of colorectal cancer mortality among men without cancer at baseline who had low social support compared to those with more social support, but no evidence of an effect among women in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁵³Ikeda A, Kawachi I et al. Social support and cancer incidence and mortality: the JPHC study cohort II. Cancer Causes & Control. 2013;24:847–60.

• 17% higher melanoma-specific mortality within 5 years among people without melanoma at baseline experiencing partner bereavement compared to those not bereaved in a very large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁵⁴Wong AYS, Frøslev T et al. The association between partner bereavement and melanoma: cohort studies in the U.K. and Denmark. British Journal of Dermatology. 2020 Oct;183(4):673-683.

• Higher risk of prostate cancer among married men compared to unmarried men in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 3 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵⁵Brown CR, Hambleton I et al; U.S. Caribbean Alliance for Health Disparities Research Group (USCAHDR). Social determinants of prostate cancer in the Caribbean: a systematic review and meta-analysis. BMC Public Health. 2018 Jul 20;18(1):900.