Derrick Lonsdale (born 1924) M.D., Fellow of the American College of Nutrition (FACN), Fellow of the American College for Advancement in Medicine (FACAM) is a pediatrician and researcher into the benefits of certain nutrients in preventing disease and psychotic behavior. Thiamine is a special vitamin because as the cause of beriberi it is one of only four vitamins associated with a named pandemic deficiency disease. Of these four vitamins, only thiamine requires transport proteins to diffuse throughout the body. A thiamine derivative called TTFD is a thiamine precursor that does not require transport proteins to freely diffuse.
Dr Lonsdale was a practitioner in pediatrics at the Cleveland Clinic for 20 years. He became Head of the Section of Biochemical Genetics at the Clinic. The Cleveland Clinic is rated as the third best hospital in the United States.
He is also on the Scientific Research Advisory Committee of the American College for Advancement in Medicine and is an editor of their Journal.
Lonsdale has studied the use of nutrients to prevent diseases and his work has been favorably reviewed.  He is particularly interested in Vitamin B1, also known as thiamine. Lonsdale's research on the effect of high doses of thiamine has been described as 'pioneering'.
- Lonsdale D, Shamberger RJ. Red cell transketolase as an indicator of nutritional deficiency. Am J Clin Nutr. 1980 Feb;33(2):205-11.
He also led a study (uncontrolled) of secretin in the treatment of autism spectrum disorder. Both of these studies are controversial because they link nutrition with autism. The study, Lonsdale D and Shamberger R J (2000) "A clinical study of secretin in autism and pervasive developmental delay." Journal of Nutritional and Environmental Medicine, Vol 10 (4), pp 271–280, has been cited by the National Autistic Society.
- Lonsdale D. Thiamine deficiency and sudden deaths. Lancet. 1990 Aug 11;336(8711):376.
- Lonsdale D. Erythrocyte transketolase activity and sudden infant death. Am J Clin Nutr. 1981 Oct;34(10):2326-7.
In 2002 Lonsdale caused controversy when he linked child violence (children killing other children) to dietary deficiencies rather than the accepted social causes. Lonsdale put this down to 'high calorie malnutrition' where children overeat high calories foods that lack vital nutrients resulting in an upset to 'brain balance'. He pointed the finger at a range of 'normal' foods as well as generally accepted junk foods. 
Lonsdale has written several books, including:
- A Nutritionist's Guide to the Clinical use of Vitamin B-1.
- Why I Left Orthodox Medicine: Healing for the 21st Century
- Free Oxygen Radicals and Disease
- A Nutritional Approach to a Revised Model for Medicine: Is Modern Medicine Helping You?
- Historical Perspectives On The Development Of Chelation Therapies
- U.S. News and World Report - 2006 Rankings
- Preventative Medicines Group - Derrick Lonsdale
- American College for Advancement in Medicine
- Encephalomyelopathy Thiamine Derivatives In Subacute Necrotizing, Journal of the American Academy of Pediatrics, Lonsdale and others
- Insight Into Copper Elimination, Dr. Paul C. Eck and Dr. Larry Wilson
- Thiamine's Mood-Mending Qualities, Richard N. Podel, Nutrition Science News, January 1999
- Treatment of autism spectrum children with thiamine tetrahydrofurfuryl disulfide: A pilot study Derrick Lonsdale, Raymond J. Shamberger 2 & Tapan Audhya</> (2002), Neuroendocrinol Lett, Vol 23:302-308.
- "Secretin and autistic spectrum disorders", The National Autistic Society
- Thiamine deficiency and its prevention and control in major emergencies, World Health Organization, 1999
- "Child Violence-Is Malnutrition the Cause?", Richard Dell' Orfano, The Weston A. Price Foundation, July 28, 2002.
- A Nutritionist's Guide to the Clinical use of Vitamin B-1 ISBN 0-943685-02-8, Amazon
- Why I Left Orthodox Medicine: Healing for the 21st Century ISBN 1-878901-98-2, Amazon
- Free Oxygen Radicals and Disease ISBN 0-87983-451-X, Amazon
- A Nutritional Approach to a Revised Model for Medicine: Is Modern Medicine Helping You? ISBN 1618970925, Amazon