Vincent Marks, who has died aged 93, was a world expert in insulin and hypoglycaemia (low blood sugar). In 1985, his expert opinion helped to acquit Claus von Bülow of attempted murder, in a case that was dramatised in the film Reversal of Fortune (1990).
On 21 December 1980, the American heiress Sunny von Bülow was discovered comatose in her bathroom, and she remained in a persistent vegetative state until her death in 2008. Her husband Claus, a Danish-born lawyer, was tried and found guilty of injecting her with insulin. On appeal in 1985, the defence showed there was no injection and, having scrutinised Sunny’s medical notes, Marks said her collapse was likely to have been triggered by alcohol-induced fasting hypoglycaemia. “Sunny,” he said, “was the victim of natural illness and her lifestyle.”
Marks’ achievements and interest in hypoglycaemia began in the late 1950s when he created ways to detect low blood sugar and researched how the pancreas and glucose-management hormones work – vital knowledge that underpins the modern treatment of diabetes.
From 1957 to 1962 he was a junior doctor in chemical pathology at the National Hospital for Neurology and Neurosurgery in London. He saw patients being diagnosed with dementia and other neurological conditions because they had confusion, anxiety and panic attacks, but they might have had hypoglycaemia, which has the same symptoms.
The existing test for low blood glucose required laboratory apparatus and technical skill, so Marks developed a simpler method for doctors to use. It relied on the enzyme glucose oxidase, which made blood samples change colour according to the concentration of glucose. It was a forerunner of the glucose strips widely used in diabetes today.
Marks worked with the South African researcher Ellis Samols to introduce a new technique from the US called insulin radioimmunoassay that could accurately measure the amount of insulin in the blood. This opened up the whole field of diabetes research. He also researched the relationship between glucagon and insulin, two hormones produced in the pancreas that keep blood glucose within a normal range, and the role of a gut-derived hormone called glucagon-like peptide-1 (GLP-1), which stimulates the pancreas to secrete insulin.
In 1962, Marks moved to Epsom in Surrey, to work as consultant chemical pathologist at West Park and Epsom District hospitals, where he set up a chemical pathology laboratory and co-wrote Hypoglycaemia (1965) which for more than 20 years was the standard medical textbook.
In 1970, he became professor of biochemistry at the University of Surrey and consultant chemical pathologist at the Royal Surrey and St Luke’s hospitals in Guildford. There he created and led a much larger laboratory that became the leading centre for insulin testing in the UK. It was also there that he founded and led the UK’s leading MSc course in clinical pathology.
Marks’ research included monitoring the level of various drugs in the blood, including lithium, and he developed an assay (a test) for the hormone melatonin and for insulin-like growth factor-1 and 2 (hormones that promote growth of bones and tissues). He was interested in how blood sugar can rise and fall in reaction to different medicines, foods and alcohol, and in 1977 wrote a paper entitled Lunchtime Gin and Tonic: A Cause of Reactive Hypoglycaemia.
He contributed to his specialty at the highest level, becoming president of the Association of Clinical Biochemists (1989-91) and vice president of the Royal College of Pathologists.
Marks was born in Harlesden, north-west London, where his father, Lewis, and mother, Rose (nee Goldbaum), ran a pub. He had a younger sister, Sheila, and an elder brother, John. War broke out in 1939 and he was billeted to a family in Devon where, being Jewish, he found he could not eat some of the food. His brother was dispatched by their father to see him, with a message that the chief rabbi said Jewish dietary rules were suspended during the war. If you could arbitrarily waive a set of religious rules, thought Marks, why not dispense with religion altogether? He was fast becoming a staunch atheist.
In 1942 Marks returned to London and attended Tottenham grammar school. He grew up in a home that had conversation around the dinner table at its heart. Discussions on medicine, politics, religion and world affairs were encouraged and throughout his life Marks loved to talk and debate.
As adults, both he and his brother John (also a doctor, and chair of the British Medical Association) had strong booming voices. According to Vincent’s son Lewis: “The telephone was simply an inconvenience when my father and his brother talked.”
In 1948 Marks won a scholarship to Brasenose College, Oxford, to study medicine. Noticing the college took every paper except the Daily Worker he inquired why and was quickly dubbed “the college communist”. After his clinical training at St Thomas’ hospital in London, he qualified in 1954. He originally wanted to specialise in psychiatry but while doing the usual rotation of junior jobs he became interested in clinical pathology and took a job at the National Hospital for Neurology and Neurosurgery.
In 1957 Marks married the sculptor and artist Averil Sherrard. The couple had two children, Alexandra and Lewis, and made their home in Surrey.
In 1995 Marks retired from his NHS and university jobs, but as an emeritus professor he continued to research and publish, reviewing one paper a day or so before he died. He also remained engaged in medico-legal work, which he wrote about with the journalist Caroline Richmond in Insulin Murders (2007). As well as his account of the trial to acquit Von Bülow, it tells of his part in securing the conviction of the nurse Beverly Allitt in 1993, who murdered four children, killing two with insulin.
Throughout his life, Marks vocally supported a number of causes. Disliking medical fraudsters, he was a founder member of HealthSense (originally HealthWatch); and he supported Dignity in Dying. At a local level, he and his wife campaigned to save a local park from developers in Guildford.
Marks is survived by Averil, Alexandra and Lewis, six grandchildren and four great-grandchildren.
• Vincent Marks, pathologist and clinical biochemist, born 10 June 1930; died 6 November 2023