Introduction: Whether or not vitamin D may lower the risk of breast cancer is under study.
Most of the vitamin D a person gets comes from the sun and a small amount comes from diet.
Findings from studies on vitamin D (through diet alone or diet plus sunlight exposure) and breast cancer risk are mixed.
Studying vitamin D with measures of sunlight exposure and diet has some challenges. It is hard to measure sunlight exposure. And, because so many foods that contain vitamin D also contain calcium, it is hard to single out the effects of vitamin D alone.
Blood levels of vitamin D are a good marker of vitamin D exposure. By studying blood levels of vitamin D, researchers avoid the measurement issues with sunlight exposure and diet.
Findings from studies on a possible link between blood levels of vitamin D and breast cancer risk have been mixed.
Learn more about vitamin D and breast cancer risk.
Learn more about vitamin D.
Learn about the strengths and weaknesses of different types of studies.
See how this risk factor compares with other risk factors for breast cancer.
Read our perspective on the vitamin D and breast cancer risk (January 2011)*.
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date at this time.
Study selection criteria: For studies with measures of sunlight exposure and dietary intake of vitamin D: Randomized controlled trials, prospective cohort studies, nested case-control studies and meta-analyses with at least 800 breast cancer cases.
For studies of blood levels of vitamin D: Prospective cohort studies and nested case-control studies with at least 500 breast cancer cases.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Sunlight Exposure and Dietary Intake of Vitamin D
Study Population (number of participants)
Measure(s) of Vitamin D
Relative Risk of Breast Cancerin Women with a High Exposureto Vitamin D Compared toWomen with Low Exposure, RR (95% CI)
Randomized controlled trials
Women’s Health Initiative 
Postmenopausal women: 1.04 (0.94-1.14)†
Prospective cohort studies
319,985 (7,760 cases)
Premenopausal women: 1.07 (0.87-1.32)
Postmenopausal women: 1.02 (0.90-1.16)
Nurses' Health Study 
Premenopausal women: 0.72 (0.55-0.94)
Postmenopausal women: 0.94 (0.80-1.10)
French E3N Cohort 
Premenopausal women: 1.03 (0.85-1.25)
Postmenopausal women: 0.92 (0.83-1.02)
Sun exposure: High vs. low level of sun exposurein place of residence
Premenopausal women: 0.85 (0.67-1.08)
Postmenopausal women: 0.92 (0.82-0.98)
Cancer Prevention Study II Nutrition Cohort 
Postmenopausal women: 0.95 (0.81-1.13)
Iowa Women’s Health Study 
Postmenopausal women: 0.89 (0.77-1.03)
Women’s Health Study 
Premenopausal women: 0.65 (0.42-1.00)
Postmenopausal women: 1.30 (0.97-1.73)
Norwegian Women and Cancer Study 
Pre- and postmenopausal women: 1.07 (0.87-1.32)
Sun exposure: More than one sunburn per year vs. none
Pre- and postmenopausal women: 0.95 (0.75-1.21)‡
VITAL Cohort 
Postmenopausal women: 0.68 (0.50-0.92)
Women’s Lifestyle and Health Cohort Study 
Pre- and postmenopausal women: 0.9 (0.8-1.1)
Sun exposure: 2 or moresunburns per yearvs. none
Pre- and postmenopausal women:1.1 (0.9-1.4)§
Chen et al. 
Pre- and postmenopausal women: 0.91 (0.83-1.00)
Kim and Je 
Pre- and postmenopausal women: 0.95 (0.88-1.01)
Gissel et al. 
Pre- and postmenopausal women: 0.98 (0.93-1.03)
Sperati et al. 
Postmenopausal women: 1.11 (0.74-1.68)
† Breast cancer risk among women randomized to take a supplement containing vitamin D and calcium versus women randomized to a placebo for 7 years (with continued follow-up).
‡ Average number of sunburns per year. Sun exposure as measured by weeks per year spent on sunbathing vacations and tanning bed use was also not related to breast cancer risk.
§ Sunburns from ages 10 to 19 years. Findings also showed other measures of sun exposure were not related to breast cancer risk including sunburns during other ages, weeks per year spent on sunbathing vacations and tanning bed use.
Blood Levels of Vitamin D
Relative Risk of Breast Cancerin Women with Higher Blood Levelsof Vitamin D (25-hydroxyvitamin D)Compared to Women with Lower Levels, RR (95% CI)
Nested case-control studies
New York University Women’s Health Study and Northern Sweden Mammary Screening Cohort 
Premenopausal women: 0.67 (0.48-0.92) Postmenopausal women: 1.21 (0.92-1.58)
Pre- and postmenopausal women: 1.07 (0.85-1.36)
Women’s Health Initiative [1,17]
Postmenopausal women: 1.06 (0.78-1.43)
Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial 
Postmenopausal women: 1.04 (0.75-1.45)
Malmo Diet and Cancer Study 
Pre- and postmenopausal women: 0.93 (0.66-1.33)
Nurses' Health Study 
Pre- and postmenopausal women: 0.73 (0.49-1.07)
French E3N Cohort 
Pre- and postmenopausal women: 0.73 (0.55-0.96)
Nurses' Health Study II 
Pre- and postmenopausal women: 1.29 (0.92-1.81)
Cancer Prevention Study-II 
Postmenopausal women: 1.09 (0.70-1.68)
14 nested case-control andcohort studies
Pre- and postmenopausal women: 0.92 (0.83-1.02)
Chen et al. 
10 nested case-control studies and 1 retrospective study
Pre- and postmenopausal women: 0.86 (0.75-1.00)
Mohr et al. 
5 nested case-control studies
Pre- and postmenopausal women: 0.87 (0.77-0.99)
U.S. Preventive Services Task Force 
4 nested case-control studies
Pre- and postmenopausal women: 0.99 (0.97-1.01)
¶ Average number of years between blood collection and breast cancer diagnosis in cases.
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