Methods are provided of identifying a subject having impaired aldehyde dehydrogenase activity; and administering to the subject a compound comprising an isotopicaliy-modified polyunsaturated fatty acid, an isotopicaliy-modified polyunsaturated fatty acid ester, an isotopicaliy-modified polyunsaturated fatty acid thioester, an isotopicaliy-modified polyunsaturated fatty acid amide, a polyunsaturated fatty acid mimetic, or an isotopicaliy-modified polyunsaturated fatty acid pro-drug, the compound having an isotopic modification that reduces oxidation of the compound, thereby reducing production in the subject of substrate for aldehyde dehydrogenase. Some aspects provide coadministering an isotopicaliy-modified polyunsaturated fatty acid and an oxylipin.