Skin fluorescence of reduced nicotinamide adenine dinucleotide in primary hypothyroidism: Association with age and body mass index

Introduction. The search for parameters reflecting the peripheral effects of thyroid hormones remains an important challenge. Fluorescence spectroscopy (FS) enables noninvasive assessment of tissue metabolism by measuring the fluorescence of reduced nicotinamide adenine dinucleotide (NADH), a key cofactor of oxidative phosphorylation. A i m. To evaluate skin NADH fluorescence parameters as potential markers of energy metabolism disturbances in patients with primary hypothyroidism and to assess their association with age and body mass index (BMI). Materials and methods . A cross-sectional study included 50 healthy volunteers and 51 patients with primary hypothyroidism(14 overt and 37 subclinical). NADH fluorescence amplitude (AF NADH ) was measured using FS in forearm skin at baseline, duringlocal cooling (10 °C), heating (35 °C and 42 °C), and during an occlusion test. Results . No differences in AF NADH parameters were observed between groups at baseline or during functional tests. The onlyfinding was a reduced relative change in AF NADH during cooling in subclinical hypothyroidism (p = 0.021). NADH fluorescenceparameters did not correlate with TSH, fT3, or fT4 after adjustment for age. In the overall sample, age was positively correlatedwith AF NADH , most strongly in healthy participants (r up to 0.51; p < 0.001). In this group, BMI was also correlated with AF NADH during thermal tests. Conclusions. Skin NADH fluorescence parameters do not change in primary hypothyroidism. However, they are associated withage, reflecting age-related alterations in cellular NADH metabolism (or fluorescence properties of the skin) and warrant furtherinvestigation. The rate of NADH utilization during heating is associated with BMI.