Tai chi—a Chinese martial art that uses graceful, fluid movements and focuses on breathing—lowers stress and boosts flexibility. But a British study recently found that it offers another benefit: raising the number of your T cells (a.k.a. CD4 cells). Participants (all had diabetes but not HIV) gained some CD4s after practicing tai chi for a 12-week period. Researchers think the secret ingredient could be the exercisers’ feelings of well-being. Find a class in your area at taichinetwork.org or tai one on at home with T’ai Chi Beginning Practice DVD (Gaiam, $15).