Australian research has shown that people with obesity are more likely to be deficient in vitamin D, but not in anaemia or vitamin B12.

The study’s authors aimed to find out how common micronutrient deficiencies and anemia are among Australian adults and how they are related to body mass index (BMI) categories.

The findings of the study were published today in BMJ open.

In their study, the researchers divided about 3500 adults into four groups based on their body mass index (BMI): healthy weight, overweight, obesity class 1, and a combined obesity class 2 and 3.

They analyzed data from the 2011-2013 Australian Health Survey from 3539 persons aged 18 and above (no known pregnancy) with measured weight and height, as well as dietary biomarkers.

Survey weights were used to estimate the prevalence of micronutrient deficiencies (vitamin B12 deficiency; serum vitamin B12; iron deficiency; ferritin; vitamin D deficiency) and anemia (haemoglobin 120 g/L for females and 130 g/L for males) and to assess associations with logistic regression models.

They then compared the nutrient levels in these groups. The results showed that those in obesity class 2 and 3 were consistently more likely to be vitamin D deficient.

The researchers suggest that this could be because these individuals spend less time outdoors.

They write: “This association is likely explained by lower levels of sun exposure among those with obesity compared with healthy weight individuals. Vitamin D production in the skin is considered the primary natural source of vitamin D. People with obesity likely have decreased exposure to the sun from spending less time outdoors33–35 and wearing sun concealing clothing.”

They also found no association between BMI and anaemia or B12 deficiency.

However, they did note that those in obesity class 1 appeared to be less likely to be iron deficient. They attribute this to the specific strategy they used to test iron levels.

They conclude: “We found consistent associations between severe obesity and vitamin D deficiency in Australian adults. We also found obesity class I was negatively associated with iron deficiency, whereas there was no consistent association between BMI groups and vitamin B12 deficiency and anaemia. Clinicians and health policymakers should be aware that severe obesity is positively associated with vitamin D deficiency in the general population. Public health strategies are needed to prevent vitamin D deficiency in this high-risk population group.”

Source: 10.1136/bmjopen-2022-061442