Hyderabad: A new study conducted by Gandhi Medical College, Secunderabad, has revealed that night shift workers at a multinational company in the city face higher insulin resistance, lower testosterone levels, and worse cholesterol profiles than their day shift counterparts.
The cross-sectional study, conducted between March 2020 and March 2022, compared 45 night shift workers with 45 day shift workers from the same company across a range of metabolic and hormonal markers to assess how shift patterns affect health. The findings point to circadian disruption as a driver of metabolic damage that operates independently of body weight.
Around 77% of night shift workers showed insulin resistance, a precursor to type 2 diabetes, compared to 62% among day shift workers. Night shift workers were also younger on average, at 28.6 years against 31.1 years, and carried lower body mass index scores of 24.2 kg/m² against 25.2 kg/m² among day workers.
The authors say this combination makes the finding particularly significant. “Night-shift work is associated with increased risk of insulin resistance, hypertriglyceridemia, low HDL-C, low LH and testosterone in males, high oestradiol among females, and vitamin D deficiency,” they write.
“There was a higher number of subjects with insulin resistance in the night shift worker group despite the lower BMI and waist circumference. This highlights the potential role of circadian misalignment and sleep disruption in driving insulin resistance,” the authors said.
High cholesterol levels raise heart disease risk
Night shift workers recorded higher triglyceride levels at 195 mg/dl against 180 mg/dl among day workers, and lower HDL, or good cholesterol, at 35 mg/dl against 40 mg/dl. Both patterns raise the risk of cardiovascular disease.
“Prior studies have conclusively demonstrated the association of night shift work with high triglycerides and low HDL-C, explaining the increased cardiovascular risk,” the authors said, situating their findings within a broader body of global research that links irregular work schedules to heart disease.
Testosterone falls, hormones shift
Male night shift workers recorded lower luteinising hormone levels at 2.8 mIU/ml against 5.6 mIU/ml among day shift males, and reduced testosterone at 373.6 ng/dl against 400 ng/dl. Female night shift workers showed elevated oestradiol levels at 181 pg/ml against 100 pg/ml among day shift women, pointing to broader hormonal disruption tied to irregular schedules.
The authors link these findings to the mechanics of circadian misalignment. “Circadian misalignment impairs hypothalamic-pituitary signalling, reduces growth hormone secretion, alters gonadal hormone regulation, and disrupts adipokine release, providing biological plausibility for our findings,” they said.
On testosterone specifically, the authors note that previous research by Bracci et al. found low testosterone levels in male shift workers and linked them to a higher risk of erectile dysfunction, a finding that aligns with their own results.
The study also recorded higher rates of subclinical hypothyroidism among night shift workers at 22% against 11% among day workers. Reduced growth hormone levels were also observed, which the authors describe as consistent with impaired nocturnal secretion, given that growth hormone is released primarily during sleep.
Vitamin D and the sunlight deficit
Night shift workers recorded significantly lower vitamin D levels at 10.4 ng/ml, compared to 13.7 ng/ml among day workers. Both groups showed low vitamin D overall, but the gap between them remained statistically significant.
“Reduced vitamin D levels in night shift workers are plausibly attributable to diminished sunlight exposure, reinforcing the occupational contribution to metabolic risk,” the authors said.
The weight paradox
One of the more striking threads running through the study is what the authors describe as a paradox. Night shift workers, despite being younger and carrying less body weight, showed worse metabolic health across multiple markers than their heavier, older day shift counterparts.
“A striking finding was that night shift workers had lower BMI and waist circumference compared with day-shift workers, but still displayed higher insulin resistance, dyslipidaemia, and altered endocrine parameters. This paradox suggests that circadian disruption exerts metabolic effects independent of overall adiposity,” the authors said.
This finding carries implications for how health risks are assessed in working populations. Standard screening tools that rely on weight or waist measurements may miss the damage accumulating in night shift workers who appear physically fit by conventional measures.
“The novelty of our findings lies in demonstrating that even with lower BMI and waist circumference, night-shift workers have significant metabolic and endocrine derangements. This underscores that body weight alone may underestimate cardiometabolic risk in this group,” the authors said.
A gap in Indian research
The authors note that very little research exists on night shift work in India, despite the scale of the workforce involved. Sectors including IT, healthcare, manufacturing, and transportation run large night shift operations across urban centres, yet the health consequences for Indian workers remain understudied.
“Few studies have assessed detailed endocrine parameters in the Indian context, where genetic susceptibility and lifestyle factors may amplify risk,” the authors said. The inclusion of markers such as adiponectin, free fatty acids, growth hormone, and IGF-1 in this study, they add, provides new insight into the biological mechanisms at work.
Call for targeted screening
The authors conclude that screening and intervention strategies for shift workers need to move beyond weight and waist measurements and address circadian and hormonal pathways directly.
“Screening and intervention strategies for shift workers must therefore go beyond anthropometric measures and address circadian and hormonal pathways,” they said.
With India’s night shift workforce expanding across sectors and cities, the study adds to growing global evidence that links irregular work schedules to long-term metabolic and hormonal damage. The authors call for occupational health strategies that treat circadian disruption as an independent and measurable risk factor, not a secondary concern.
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