The studies looked at the physiological and psychological health of 45 men who worked on offshore oil rigs. The research showed split-shift workers had overly high levels of fatty acids in their blood after meals, compared with same-shift workers.
Split-shift employees worked one week day shifts and one week night shifts, while same-shift workers worked only day or night shifts.
The studies also showed split-shift workers had low levels of sleep hormone melatonin, leaving them more tired and prone to making mistakes on the job.
One study was done by chronobiologist Josephine Arendt and her team at the University of Surrey and one study by psychologist Andrew Smith and his colleagues at the University of Cardiff in Wales.