Vitamin D for Cancer

Vitamin D for Cancer: Safety & Side Effects

This page covers safety information for Vitamin D. See our complete Vitamin D therapy guide →

Author

Nancy Hepp, MS

past Lead Researcher

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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS past Lead Researcher

Reviewer

Laura Pole, MSN, RN, OCNS

Senior Clinical Consultant

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Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.

For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.

Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.

Laura Pole, MSN, RN, OCNS Senior Clinical Consultant

Last update: May 4, 2026

Is vitamin D safe?

Vitamin D is generally considered safe at moderate levels. Be sure to get your levels tested and discuss with your healthcare provider before supplementing.

Risk of cancer

Some higher risks of cancer are seen among people with higher vitamin D intake or 25(OH)D levels above about 40 ng/mL (100 nmol/L). The evidence looking at this can be complicated to draw conclusions from given potential confounders like sun exposure or interactions with calcium supplementation, but the overall evidence does suggest very high levels of vitamin D can be associated with increased cancer risk. You can review the evidence in detail on our evidence page. These observations further enforce the importance of supplementing based on blood work with the guidance of a health care provider.¹Freedman DM, Looker AC, Abnet CC, Linet MS, Graubard BI. Serum 25-hydroxyvitamin D and cancer mortality in the NHANES III study (1988-2006). Cancer Research. 2010 Nov 1;70(21):8587-97; Cauley JA, Chlebowski RT et al. Calcium plus vitamin D supplementation and health outcomes five years after active intervention ended: the Women’s Health Initiative. Journal of Women’s Health. 2013 Nov;22(11):915-29; Zgaga L, O’Sullivan F et al. Markers of vitamin D exposure and esophageal cancer risk: a systematic review and meta-analysis. Cancer Epidemiology, Biomarkers & Prevention. 2016 Jun;25(6):877-86; Chen GC, Zhang ZL et al. Circulating 25-hydroxyvitamin D and risk of lung cancer: a dose-response meta-analysis. Cancer Causes and Control. 2015 Dec;26(12):1719-28; Freedman DM, Looker AC, Abnet CC, Linet MS, Graubard BI. Serum 25-hydroxyvitamin D and cancer mortality in the NHANES III study (1988-2006). Cancer Research. 2010 Nov 1;70(21):8587-97; Stolzenberg-Solomon RZ, Jacobs EJ et al.Circulating 25-hydroxyvitamin D and risk of pancreatic cancer: Cohort Consortium Vitamin D Pooling Project of Rarer Cancers. American Journal of Epidemiology. Jul 1 2010;172(1):81-93; Liu Y, Wang X, Sun X, Lu S, Liu S. Vitamin intake and pancreatic cancer risk reduction: a meta-analysis of observational studies. Medicine (Baltimore). 2018 Mar;97(13):e0114; Xu Y, Shao X et al. Positive association between circulating 25-hydroxyvitamin D levels and prostate cancer risk: new findings from an updated meta-analysis. Journal of Cancer Research and Clinical Oncology. 2014 Sep;140(9):1465-77; Kristal AR, Till C et al. Plasma vitamin D and prostate cancer risk: results from the Selenium and Vitamin E Cancer Prevention Trial. Cancer Epidemiology, Biomarkers and Prevention. 2014 Aug;23(8):1494-504; Gilbert R, Martin RM e tal. Associations of circulating and dietary vitamin D with prostate cancer risk: a systematic review and dose-response meta-analysis. Cancer Causes and Control. 2011 Mar;22(3):319-40; Huncharek M, Muscat J, Kupelnick B. Dairy products, dietary calcium and vitamin D intake as risk factors for prostate cancer: a meta-analysis of 26,769 cases from 45 observational studies. Nutrition and Cancer. 2008;60(4):421-41; Weinstein SJ, Mondul AM et al. Prediagnostic serum vitamin D, vitamin D binding protein isoforms, and cancer survival. JNCI Cancer Spectrum. 2022 Mar 2;6(2):pkac019.

Side effects and adverse reactions

Vitamin D is a fat-soluble vitamin with a risk for toxicity and overdose from taking extremely high doses of supplements. Research has shown that 60,000 IU per day leads to vitamin D toxicity.²Zeratsky K. What is vitamin D toxicity? Should I be worried about taking supplements? Mayo Clinic. Viewed July 13, 2022. ​​Acute toxicity could be caused by doses of vitamin D probably in excess of 10,000 IU/day over long periods.³Marcinowska-Suchowierska E, Kupisz-Urbańska M, Łukaszkiewicz J, Płudowski P, Jones G. Vitamin D toxicity-a clinical perspective. Frontiers in Endocrinology (Lausanne). 2018 Sep 20;9:550; De Vincentis S, Russo A et al. How much vitamin D is too much? A case report and review of the literature. Endocrine, Metabolic and Immune Disorders Drug Targets. 2021;21(9):1653-1659. We advise medical supervision if you plan to take high doses of supplements (more than 4000 IUs per day). Overdose is unlikely when getting vitamin D from food sources or sun exposure.

Although once rare, vitamin D toxicity has increasingly been reported in people with serum concentrations ranging between 150 and 1220 ng/mL and serum calcium concentrations between 11.1 and 23.1 mg/dL. Such high levels are typically seen among people taking high doses of vitamin D supplements, with underlying causes including manufacturing errors and/or overdosing by patients or prescribers.⁴Galior K, Grebe S, Singh R. Development of vitamin D toxicity from overcorrection of vitamin d deficiency: a review of case reports. Nutrients. 2018 Jul 24;10(8):953; Lim K, Thadhani R. Vitamin D toxicity. Brazilian Journal of Nephrology. 2020 Apr 3;42(2):238-244.

Adverse reactions and drug interactions are noted with high 25(OH)D levels, especially at or above 40 ng/mL (100 nmol/L).

• Vomiting or changes in bowel movements⁵Cleveland Clinic. Vitamin D Toxicity (Hypervitaminosis D). February 21, 2023. Viewed May 4, 2026.
• Drowsiness, and in extreme cases, depression, delusions and even coma⁶Cleveland Clinic. Vitamin D Toxicity (Hypervitaminosis D). February 21, 2023. Viewed May 4, 2026.
• Calcinosis (the deposit of calcium salts in tissues such as the kidneys, heart or lungs) and high blood levels of calcium (hypercalcemia);⁷National Cancer Institute. Vitamin D and Cancer Prevention. October 21, 2013. Viewed November 2, 2021. in severe cases, this can lead to the formation of kidney stones or calcifications in organs⁸Cleveland Clinic. Vitamin D Toxicity (Hypervitaminosis D). February 21, 2023. Viewed May 4, 2026.
• Acute renal failure and vitamin A toxicity⁹Granado-Lorencio F, Rubio E et al. Hypercalcemia, hypervitaminosis A and 3-epi-25-OH-D3 levels after consumption of an “over the counter” vitamin D remedy. A case report. Food and Chemical Toxicology. 2012 Jun;50(6):2106-8.

No adverse effects on reproductive hormone levels among postmenopausal women with stage 1–3a breast cancer treated with 4000 IU compared 600 IU.

• Comparable effects on reproductive hormone levels among postmenopausal women with stage 1–3a breast cancer treated with 4000 IU or 600 IU vitamin D₃ daily for 6 months in a mid-sized uncontrolled trial; the researchers concluded that the higher dose did not adversely affect reproductive hormone levels¹⁰Shapiro AC, Adlis SA et al. Randomized, blinded trial of vitamin D₃ for treating aromatase inhibitor-associated musculoskeletal symptoms (AIMSS). Breast Cancer Research and Treatment. 2016 Feb;155(3):501-12.

Contraindications and precautions

Individuals with calcium metabolism disorders, gastrointestinal disease, kidney disease, heart disease, or liver disease should consult a physician before using vitamin D supplements.

Drug interactions 

There are known drug interactions with this therapy. Interactions with medications and other interventions are complex. Always consult with a healthcare professional before adding any new therapy to your regimen. To learn more about interactions visit one of the trusted resources below: 

• EfficaSafe ›
• About Herbs ›

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