1. The study, published in the Lancet recently, revealed that people living in democratic countries live longer than those who don't; they also have less of a chance of dying from heart disease, strokes, and even road accidents.
2. Incredible as it may sound, we are now told that democracy is not just good for the soul, it is good for the body too.
3. Without pressure from voters or foreign-aid agencies, dictators have less incentive to finance more expensive prevention and treatment of heart disease, cancers, and other chronic illnesses.
4. The study suggests that elections and the health of the people are increasingly inseparable.
5. A study spanning 170 countries found a strong correlation between health and the most progressive form of government.

From the first impressions, it appears that the paragraph is talking about the health of people who live in democratic nations and how it differs from those who live in non-democratic nations. It also is clear that either of sentence 2 or sentence 5, which are the most general, should start the sentence. Sentence 5 does not mention democracy, but guises it as 'the most progressive form of government', this means that 5 should start the sentence. Sentence 2, since it is not the starting sentence, should have something to refer back to as 'the sound' that it mentions. Sentence 1 is the most suitable precedent to sentence 2. Sentence 4 refers to 'the study', therefore, it cannot follow sentence 2 or sentence 3 and must follow sentence 5. We therefore have two pairs, 54, and 12, with 54 starting the paragraph. Sentence 3 talks about voters and dictators, it must come at the end because immediately after elections in sentence 4, democratic countries in sentence 1 should be mentioned. 54123 is the most suitable sequence.