He always makes light of his health issues, which worries his family.

make 是动词，意思是"做、使成为"，在这里构成固定搭配。 light 在这里是名词，本义是"光、光线"，引申为"轻松、不严肃"的意思。 of 是介词，表示"关于"。 make light of 是固定短语，意思是"轻视、对...不以为然"，指对重要的事情表现得漫不经心。