There are four leading candidates in a race that is still too close to call. Sunday's voting will be followed by a runoff on May 7 between the top two candidates.
According to the research, greying of hair and atherosclerosis portray mechanisms like impaired DNA repair, oxidative stress, inflammation, hormonal changes and senescence of functional cells.
SBS's "Saimdang, Light's Diary" and MBC's "Radiant Office," which air during the same time slot, received 8.3 percent and 6.7 percent ratings, respectively.
Following the controversy, the Singapore Tourism Board (STB) has hit back at the makers of the series with an array of photographs on its Facebook page.