Vitamin D influences the body's neurocognitive and cardiovascular systems, and insufficient vitamin D has been associated with several psychiatric disorders, such as autism, dementia and depression.
Schizophrenia patients also tend to have low levels of the vitamin, and a lack of vitamin D in utero has been found to predict later risk of the condition.
As such, researchers in South Korea and Australia conducted a study to determine the link between vitamin D and metabolic syndrome in patients with psychotic disorders.
Clear link, unclear mechanisms
They recruited 302 community-dwelling patients with psychotic disorders and recorded their clinical and sociodemographic characteristics, including blood pressure, physical activity, and dietary habits.
They then assessed their vitamin D status, lipid profile, fasting plasma glucose, glycated haemoglobin, liver function, and renal function.
The researchers subsequently noted that of the 302 study subjects, 236 (78.1%) had insufficient levels of vitamin D, and 97 (32.1%) had metabolic syndrome.
In addition, vitamin D insufficiency showed a significant association with metabolic syndrome and hypertension, as well as marked increases in triglyceride and alanine transaminase levels.
These findings remained the same even after adjustment for dietary habit and physical activity scores.
However, the researchers also wrote that though there was a clear association between vitamin D insufficiency and metabolic syndrome and especially high blood pressure, "the nature, direction and implications of this association are unclear".
Further intervention needed
The limitations of the study included its cross-sectional design, which meant the causal relationship between vitamin D and metabolic syndrome could not be investigated.
The researchers had also relied on self-reported data to assess depressive symptoms, dietary habits and physical activity, and did not administer a formal scale to measure psychotic symptoms, or look into the participants' consumption of vitamins and supplements.
Another confounding factor was the season during which the study was conducted, which was late fall and early winter.
During this period, vitamin D levels might have been lower than at other times of the year due to shorter daylight hours and therefore, less sun exposure, the latter of which was also not assessed.
In conclusion, the researchers wrote: "Nevertheless, this study has important clinical and research implications by showing that vitamin D insufficiency was very prevalent and associated with metabolic syndrome and hypertension in South Korean patients with psychosis.
"Further longitudinal and interventional studies are required in patients with psychosis."
Source: Psychiatry Investigation
"Association Between Vitamin D Insufficiency and Metabolic Syndrome in Patients With Psychotic Disorders"
Authors: Taeyoung Yoo, et al.