Study: High vitamin D levels at breast cancer diagnosis may be associated with a better prognosis

IN DEPTH REVIEW OF RESEARCH

Study background:

Previous studies have tried to determine whether there are potential associations between vitamin D levels in the blood and breast cancer risk, but have concluded with mixed results: some say there is an association while others say there is not. But fewer studies have looked at whether there is an association between vitamin D blood levels at the time of diagnosis and breast cancer prognosis; studies that did involve this relationship assessed overall survival, but not deaths from breast cancer.  As vitamin D deficiencies have known effects beyond any role in breast cancer, lower overall survival in women with low blood levels of vitamin D may be due to causes unrelated to their breast cancer.

Song Yao and colleagues from the Department of Cancer Prevention and Control at the Rosewell Park Cancer Institute performed a prospective study (meaning they designed the study and collected the data themselves rather than looking back on information collected by others or relying on patients’ recollections). They looked at the association between blood vitamin D levels at the time of diagnosis and breast cancer prognosis.

Researchers of this study wanted to know:

Does a woman’s amount of vitamin D in her blood indicate how well she will do after a breast cancer diagnosis?

Population(s) looked at in the study:

This study (called the Pathways Study) included 1,666 women who were diagnosed with invasive breast cancer. This population was established at Kaiser Permanente Northern California and was designed to specifically study factors that are associated with breast cancer recurrence and survival. The women’s vitamin D levels were measured shortly after diagnosis and were then followed for up to 96 months after they were enrolled in the study in which researchers tracked participants’ health outcomes.

Vitamin D has several forms in the blood. In this study, the researchers measured a form called 25-hydroxyvitamin D, which according to the National Institutes of Health (NIH) is the best indicator of a person’s overall vitamin D status.

The NIH states that a vitamin D level of 20 ng/mL or greater is considered adequate for bone and overall health. For this study, the researchers divided the women into three groups based on their  vitamin D blood levels:

• Group 1 had low vitamin D levels: below 16.75 ng/mL
• Group 2 had vitamin D levels just over or under the recommended levels: 16.75-25.09 ng/mL
• Group 3 had high vitamin levels: 25.10 ng/mL or greater

Study findings: 

1. Women with the highest level of vitamin D (slightly higher than the recommended vitamin D levels) in their blood had better overall survival than women with lower vitamin D levels.
   • This association was greatest in premenopausal women.
2. Premenopausal women with the highest vitamin D levels were less likely to die from breast cancer within the period of the study than women with lower vitamin D levels..
3. Premenopausal women with the highest vitamin D levels had greater invasive disease-free survival, which included recurrences and secondary cancer diagnoses, than women with lower vitamin D levels.
4. Lower vitamin D levels were associated with a more advanced stage of breast cancer at diagnosis.

Limitations:

It is important to understand that the link identified in this study between high vitamin D levels in the blood and better breast cancer survival after diagnosis does not necessarily mean that vitamin D directly caused the better prognosis or that having higher levels of vitamin D in the blood prevents breast cancer diagnosis or recurrence. Other factors that were not measured by the study may have played a role in the women’s improved survival.  

Conclusions:

This study suggests that women who are diagnosed with breast cancer and have high levels of vitamin D have a better prognosis than women with lower levels of vitamin D. More work needs to be done to further understand how this can help women with breast cancer in the clinic. In the meantime, women should maintain a healthy vitamin D level, which benefits their overall health.

Posted 1/10/17

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