Complete fatty degeneration of thymus associates with male sex, obesity and loss of circulating naïve CD8 + T cells in a Swedish middle-aged population.
Level 4 - case-series / case-control
Cross-sectional observational study
PubMed 37653480 · doi:10.1186/s12979-023-00371-7
What was done
A cross-sectional study analyzed 1,048 randomly selected Swedish adults aged 50–64 years (49% female). Computed tomography (CT) was used to measure thymic attenuation, size, and fat-to-soft-tissue ratios using a 4-point scale (0–3). Researchers evaluated associations between thymic fatty degeneration and demographic, lifestyle, and clinical factors, as well as circulating naive T cells and thymic output via T-cell receptor excision circle (TREC) levels.
What was found
Complete fatty degeneration of the thymus was observed in 59% (615/1,048), predominantly fatty attenuation in 25% (259/1,048), mixed fatty and soft tissue in 10% (105/1,048), and predominantly solid soft-tissue thymus in 6.6% (69/1,048). Age, male sex, higher BMI, abdominal obesity, and low dietary fiber intake independently associated with complete fatty degeneration. Thymic fatty degeneration and low CT attenuation also independently related to lower proportions of naive CD8+ T cells, which correlated with lower TREC levels. Specific effect sizes and confidence intervals were not reported in the abstract.
Why it matters
This study shows that CT-assessed thymic involution is common in middle-aged adults and reflects functional immunosenescence, specifically the loss of naive CD8+ T cells and reduced thymic output. It identifies potentially modifiable lifestyle factors, such as obesity and low fiber intake, that correlate with accelerated thymic aging.
Limits
The cross-sectional design cannot establish causality or temporal direction between metabolic factors and thymic involution. The sample was restricted to Swedish adults aged 50–64 years. Statistical effect sizes, odds ratios, and p-values were omitted from the abstract.
Cited by
- supports T cells mature in the thymus, which involutes over time to the point where individuals in their 40s through 70s may have virtually no thymic tissue.