Lung cancer is the leading cause of cancer-related mortality in the United States, accounting for approximately 1 out of 4 cancer deaths. According to the American Cancer Society, more people are killed by lung cancer each year than by breast, colon and prostate cancer combined.
While lung cancer is not completely preventable, avoiding certain behaviors help decrease the risk of developing the disease. These modifiable risk factors include smoking, exposure to secondhand smoke, lack of physical activity and an unhealthy diet.
Additionally, recent research has discovered a potential role of vitamin D in the prevention of cancer and cancer mortality. Vitamin D is involved in mediating cell proliferation and differentiation, which are functions of the cell, which can lead to tumor growth when uncontrolled. According to researchers, this may be a mechanism by which vitamin D plays a role in cancer prevention and survival.
In 2015, two meta-analyses by Zhang et. al. and Chen et. al. found that there was an inverse relationship between vitamin D levels and risk of lung cancer. However, the effect of vitamin D specifically on the prognosis and mortality rate of lung cancer patients is not clear. Therefore, researchers from this study conducted a systematic review and meta-analysis to determine the relationship between vitamin D, lung cancer risk and mortality.
A total of 22 studies and 813,801 participants were included in this meta-analysis. Of these studies, six were case-control studies, which compared patients with lung cancer to matched controls. The remaining 16 were cohort studies that analyzed lung cancer prevalence from the general population. All the participants were categorized by their vitamin D status.
This is what the researchers found:
- There was a decreased lung cancer risk in patients with higher vitamin D levels compared to those with lower vitamin D levels (p<0.05).
- After adjusting for confounding variable, reduced odds of lung cancer diagnosis was associated with increased vitamin D intake (OR=0.92; 95% CI: 0.85–1.00). In addition, there was a negative association between lung cancer risk in nonsmokers and vitamin D intake (p<0.01), but no association between vitamin D intake and lung cancer risk in past or current smokers (p=0.92 and p=0.85, respectively).
- Higher circulating vitamin D levels were associated with increased odds of survival and a decreased risk of mortality (OR: 1.01; 95% CI: 0.87–1.18 and OR = 0.39, 95% CI: 0.28–0.54, respectively).
The researchers concluded:
“Our meta-analysis suggests that higher serum 25(OH)D and vitamin D intake is negatively linked with lung cancer incidence.”
The researchers addressed the study’s limitations. First, some of the studies varied slightly in the consistency of the time of collection, quantity of the sample collected and season of collection. The type of analysis used to determine serum 25(OH)D levels also varied. In addition, some of the papers utilized in this meta-analysis were of observational design, therefore, limiting evidence of any causal relationship between vitamin D levels and lung cancer.
Despite these weaknesses, this study did have some significant strengths, such as the enormous study population. Also, the researchers did report that no significant heterogeneity was found, meaning that no major differences between the studies were found that may render them incomparable. Overall, this study confirmed past findings regarding the relationship between vitamin D and lung cancer. RCTs are needed to confirm the relationship between vitamin D, lung cancer risk and prognosis.
Peterson, R. & Cannell, JJ. Meta-analysis discovers vitamin D levels are associated with lung cancer risk and survival, 7/2017.