Genetics is only part of the answer, Majid Ezzati, who runs the NCD study at Imperial College London, told BBC News.
Speaking of how national average heights change over decades, he said: "About a third of the explanation could be genes, but that doesn't explain the change over time.
"Genes don't change that fast and they don't vary that much across the world," he said, adding: "So changes over time and variations across the world are largely environmental."
Environmental factors such as poor diet are likely part of the answer, according to the BBC, citing a study that found a 20cm (7.9 in) difference between children in the tallest and shortest nations.
It could also help explain why average heights in several nations have both risen and fallen over the last decades — while nations like Japan, South Korea and China have seen height increases, some sub-Saharan African nations like Uganda and Sierra have seen male height decreases, the BBC reported.