In this study, 272 diabetic retinopathy patients, 190 diabetic patients without retinopathy, and 285 non-diabetic healthy controls were assessed for their history of diabetes, lifestyle information, and health status.
They also underwent ocular and anthropometric examinations, and laboratory tests. Fasting blood samples were collected from all participants to check for the carotenoid levels, using high-performance liquid chromatography (HPLC).
The levels of β-carotene were statistically significantly lower in patients suffering from diabetes mellitus.
Meanwhile, lower concentrations of α-carotene were displayed in non-smokers with diabetic retinopathy non-smoker.
The level of β-cryptoxanthin and lycopene were also lower in diabetes mellitus and diabetes retinopathy group respectively, however both were not statistically significant.
The researchers, from Beijing Tongren Hospital and Sun Yat-sen University, Guangzhou, wrote: "This cross-sectional study among (a) Chinese urban population showed that serum β-carotene may have a protective effect on diabetes, while α-carotene appears to be a protective factor for diabetic retinopathy in non-smokers."
"Our findings support the hypothesis that eating a diet rich in antioxidant carotenoids might help prevent the development of type 2 diabetes. Though carotenoids may also be beneficial for diabetic retinopathy, quitting smoking is the precondition of the benefits.
"However, further evidence from epidemiological research is needed before a definitive conclusion on this issue can be drawn."
Prior to the above findings, this group of researchers revealed that a diet rich in carotenoids could contribute to the prevention of type 2 diabetes, provided a non-smoking healthy lifestyle is also observed.
The findings were welcomed by Bryan See, business development manager at tocotrienol and mixed-carotene supplier ExcelVite.
"One in every 11 adults is now suffering from diabetes, according to the International Diabetes Federation. That figure is 10 million more than the number in 2015. Urgent action has to be taken to control this alarming increase," he said.
"Back in 2016, a cohort study was published in British Medical Journal's Open Diabetes Research and Care that demonstrated a long-term high consumption of carotenoids, especially pro-vitamin A carotenoids, could reduce the risk of type 2 diabetes in middle-aged and older Japanese patients.
"We welcome this research, which further supports the protective effect of α-carotene and β-carotene on diabetes mellitus and diabetes retinopathy, respectively."
Source: Current Molecular Medicine.
"Serum carotenoids and risks of diabetes and diabetic retinopathy in a Chinese population sample"
Authors: C. She, et al.