Vitamin D supplementation to prevent breast cancer? Experts weigh in on controversial study

23 Jan 2020 --- Pakistani women with a vitamin D deficiency (VDD) have a higher risk of breast cancer, while women with a history of vitamin D supplementation are less at risk. This is according to a recent study that has explored the association between vitamin D intake and breast cancer, as well as more affordable cancer prevention measures for women lacking access to resourced health systems. As cancer rates and the financial burdens of its treatments increase worldwide, the discussion surrounding the doubts and benefits in the vitamin D supplementation space continues.

The study’s lead researcher Dr. Uzma Shamsi, Assistant Professor at the University of Adelaide, Australia and Aga Khan University, Pakistan, tells NutritionInsight that this research was motivated by the observed vitamin D deficiency and breast cancer prevalence increases in Pakistani women. 

The study examined a total cohort of 411 newly diagnosed histologically confirmed primary breast cancer cases and 784 control subjects, from two hospitals in Karachi, Pakistan. 

VDD was significantly more frequent in breast cancer cases, with nearly 40 percent of breast cancer cases categorized as severe VDD, compared to 33 percent of controls. Meanwhile, 29 percent of breast cancer cases were classified as deficient compared to 24 percent of controls. Vitamin D sufficiency was higher among controls (25 percent) compared to cases (17 percent).

The use of vitamin D supplement (both injections and oral), was assessed in relation to the index year, defined as one year prior to breast cancer diagnosis for cases or the interview for controls. Notably, vitamin D deficient women, compared with vitamin D sufficient women, were significantly more likely to be in the 35 to 44-year age group, premenopausal and of lower socio-economic status.

As vitamin D supplementation may help reduce the risks of breast cancer, this research is particularly significant for women living in countries who may have limited access to health facilities that could provide them with cancer diagnosis and management. 

In favor of supplementation
This study has brought about a peer discussion on the benefits of vitamin D supplementation. Commenting on the study, Dr. Zaki Hassan-Smith, Consultant Endocrinologist at the University Hospitals Birmingham, advocates for its usage. 

“In those with risk factors for VDD – including low sunlight exposure – should consider maintenance supplementation as it can be helpful in children to prevent rickets. People with conditions such as osteoporosis are also advised to ensure that their vitamin D status is optimized.”

Vitamin D comes from more than one source, but not all are always easily available.Vitamin D supplementation has been linked previously to cancer prevention, contributing to slowing the growth of melanoma cells, according to an earlier University of Leeds study. Research from the University of Sheffield also revealed that vitamin D oral spray is as efficacious as a capsule format, which can help patients safely choose between delivery formats, without risking developing health complications from vitamin D deficiencies.

A cautious approach
Dr. Inez Schoenmakers, Senior Lecturer, Department of Medicine, Norwich Medical School, UEA, states that she was “surprised” by the study’s findings, but notes that its results may vary when replicated in a different geographical setting.

“Unique about this study is that was conducted in women with relatively low sunshine exposure due to their dress style. As a result, these women will be mostly dependent on oral sources of vitamin D. This may differ from studies in more Western populations, where the vitamin D produced in the skin under the influence of sunshine is – for many – an important contributor to their vitamin D supply.”

Naturally occurring in the body as a response to sun exposure, vitamin D provides a range of health benefits, from physiological to mental health. Sun exposure may be the easiest way to obtain healthy levels of vitamin D, but not always the most feasible.

Dr. Shasmi explains that Pakistani women, in particular, are prone to have VDD due to a lack of sun exposure and sun avoidance behavior, as well as having darker skin tones. Multiple other factors, such as pollution and genetics, may also play a role.

Further studies
While the study seems promising, Dr. Zaki Hassan-Smith, Consultant Endocrinologist at the University Hospitals Birmingham, UK, heeds caution with the study’s findings. “The clinical significance of VDD is not addressed by the study design. It is unable to assess whether vitamin D supplementation would prevent breast cancer or improve outcomes,” he warns. 

Both he and Dr. Andrea Darling, Postdoctoral Research Fellow, Department of Nutritional Sciences, University of Surrey, UK, encourage more vitamin D supplementation trials to reassess whether higher vitamin D levels reduce the risk of breast cancer.

Dr. Shamsi affirms that with funding, a follow-up cohort study with international collaboration may be on the drawing table. Until then, she redirects the focus to sensible sun exposure more than vitamin D supplementation, while the study recommends consuming foods that contain or are fortified with vitamin D, as well as the use of vitamin D supplements.

By Anni Schleicher