MOSCOW—Police arrested nearly 1,500 people Wednesday during a day of demonstrations throughout Russia calling for freedom for imprisoned opposition leader Alexei Navalny, whose health reportedly is in severe decline after three weeks of hunger striking, according to a group that monitors political detentions. The largest of the protests took place in Moscow, where thousands marched through the center city. Some of the people arrested were seized before the protests even began, including to top Navalny associates in Moscow. Navalny’s team called for the unsanctioned demonstrations after weekend reports that his health is deteriorating and his life was in danger. “The situation with Alexei is indeed critical, and so we moved up the day of the mass protests,” Vladimir Ashurkov, a close Navalny ally and executive director of the Foundation for Fighting Corruption, told The Associated Press. “Alexei’s health has sharply deteriorated, and he is in a rather critical condition. Doctors …