A meta-analysis combining 23 studies on vitamin D supplementation found no overall reduction in mortality among general populations. However, subgroup analysis revealed significant benefits for individuals who were vitamin D deficient at baseline. Researchers conclude that supplementation may help those with deficiencies but provides little benefit to those with adequate levels.
The passage suggests that
vitamin D supplements are harmful to everyone
the effectiveness of supplements may depend on an individual's baseline nutritional status
meta-analyses cannot provide useful information
all participants in the studies were vitamin D deficient
Correct Answer: B
Choice B is the best answer. Deficient people benefited; non-deficient didn't.
- Context clues: "Significant benefits for individuals who were vitamin D deficient"; "little benefit to those with adequate levels."
- Meaning: Starting condition determines whether supplementation helps.
- Verify: The contrast between subgroups shows baseline status matters.
💡 Strategy: When effects differ by starting condition, infer that baseline status moderates outcomes.
Choice A is incorrect because deficient individuals showed "significant benefits." Choice C is incorrect because the meta-analysis revealed important subgroup differences. Choice D is incorrect because there were both deficient and adequate-level participants.