Vitamin D deficiency is endemic in the UK and northern US. It is independently associated with lower testosterone. Clinical evidence, correct dose and supplementation guidance.
Vitamin D deficiency affects an estimated 40-50% of UK adults and is independently associated with lower testosterone levels in published research. A published RCT (Pilz et al., 2011) found Vitamin D3 supplementation at 3,332 IU daily significantly increased testosterone in deficient men over 12 months.
Vitamin D receptors (VDRs) are present on Leydig cells — the testicular cells responsible for testosterone production. This suggests a direct role for Vitamin D in testosterone biosynthesis. Multiple cross-sectional studies have found significant positive correlations between serum 25(OH)D levels and testosterone.
Vitamin D is primarily synthesised in the skin via UVB sunlight exposure. In the UK, adequate UVB exposure is only available from approximately April to September — leaving most adults deficient for half the year. NICE recommends 10mcg (400 IU) daily for all UK adults — but research suggests 2000-4000 IU is required to restore deficient individuals to optimal levels.
Testosil® and TestRX® both contain Vitamin D3 alongside their core testosterone-supporting ingredients — addressing the common Vitamin D deficiency that independently suppresses testosterone in many men.