SAMe (S-adenosylmethionine) is a metabolite present in all living cells. It functions as a donor of methyl groups in over 100 different reactions and contributes to the synthesis, activation and/or metabolism of hormones, neurotransmitters, nucleic acids, phospholipids, and proteins. Methyl groups act as a signal throughout the body, regulating genetic expression and cellular function. SAMe also promotes healthy mood balance, as indicated in over 40 clinical studies. In a meta-analysis involving 25 controlled trials and 791 individuals, SAMe offered statistically significant support for positive mood, believed to be due to its support for neurotransmitter monoamine synthesis and function, including dopamine and serotonin. It also promotes healthy protein turnover and maintains healthy phospholipid methylation to support phosphatidylcholine production and cellular membrane integrity and fluidity. Studies suggest it supports joint flexibility and comfort in individuals with osteoarthritis as well. In a meta-analysis involving 11 studies, SAMe offered statistically significant support for joint function. It is believed to relieve osteoarthritis pain by supporting proteoglycan synthesis, as well as helping to stabilize and protect the proteoglycans.