A graduate student conducting research on the association between vitamin D₃ supplementation and cancer is reviewing the abstract of a recently published journal article. Which of the following conclusions can be drawn from the results of the study? A)BMI modifies the effect of vitamin D₃ on metastatic cancer B)Only BMI ≥30 kg/m² is significantly associated with an increase in metastatic cancers C)The effect of vitamin D₃ on cancer mortality is significant only for certain individuals D)Vitamin D₃ is significantly associated with a reduction in cancer mortality regardless of BMI level

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Quizplus · Accepted Answer

Explanation: 11ec2b69_c0e9_c90f_8f63_e9a9c971172e_MD0005_00 This study evaluated the association between vitamin D₃ supplementation and advanced (metastatic or fatal) cancer among adults without a diagnosis of cancer at baseline. The initial results (ie, unstratified analysis) show that vitamin D₃ is associated with a significant reduction in metastatic or fatal cancers compared with placebo (HR: 0.83, 95% CI: 0.69-0.99). A subsequent stratified analysis was conducted based on participants' BMI to determine whether BMI level (categorized as <25 kg/m², 25-29 kg/m², or ≥30 kg/m²) helps explain these associations. The stratified analysis shows that some of these associations were inconsistent across BMI level. In individuals with BMI <25 kg/m², vitamin D₃ was significantly associated with cancer mortality because the CIs excluded the null value of HR = 1 (95% CI: 0.39-0.86). However, vitamin D₃ was not significantly associated with metastatic cancers because the CI included the null value (95% CI: 0.38-1.05). In individuals with BMI 25-29 kg/m², vitamin D₃ was not significantly associated with metastatic cancer or cancer mortality because all CIs included the null value (95% CI: 0.52-1.23 for metastatic cancer; 95% CI: 0.64-1.23 for cancer mortality). Among individuals with BMI ≥30 kg/m², vitamin D₃ was not significantly associated with metastatic cancer or cancer mortality because all CIs included the null value (95% CI: 0.42-1.89 for metastatic cancer; 95% CI: 0.75-1.76 for cancer mortality) (Choice B). Therefore, the effect of vitamin D₃ supplementation on cancer mortality is modified by BMI level-that is, BMI level is an effect modifier (Choice D). Effect modification (interaction) occurs when an extraneous variable called an effect modifier (eg, BMI) changes the effect that an exposure (eg, vitamin D supplementation) has on an outcome (eg, cancer mortality) in certain groups of individuals but not others. A stratified analysis based on the modifier can help detect effect modification because it typically shows different effects in each stratum. (Choice A) There is no significant association between vitamin D₃ supplementation and metastatic cancer at any BMI level because all CIs include the null value of HR = 1. Therefore, BMI does not modify the effect of vitamin D₃ supplementation on metastatic cancer. Educational objective: Effect modification occurs when the magnitude or direction of the effect of the independent variable on the dependent variable (outcome) varies depending on the level of a third variable (effect modifier). Separate (stratified) analyses should be conducted for each level of the effect modifier.

A Graduate Student Conducting Research on the Association Between Vitamin