The Gut-Agni-Vitamin D Axis: An Integrative Review of Siddha Tikshnaagni (Digestive Fire) and Vitamin D Bioavailability

Abstract

Vitamin D deficiency is widely prevalent despite adequate dietary intake and supplementation in many populations. Vitamin D was selected because it is a global health concern, as adequate absorption depends on efficient digestion and fat metabolism, making it sensitive to variations in digestive function. Despite adequate sunlight and dietary intake, deficiency remains common, suggesting that impaired absorption and metabolic processing may reduce its biological availability. As a hormone-like nutrient essential for bone health, immunity, and metabolic balance, even small reductions in Vitamin D bioavailability can have significant health effects, making it a suitable model for exploring the influence of digestive function on micronutrient utilization. Modern research has emphasized nutrient absorption and bioavailability as critical determinants of nutritional status, especially for fat-soluble vitamins such as Vitamin D. Modern nutritional science recognizes gastrointestinal function as a major determinant of Vitamin D bioavailability because of its fat-soluble nature and dependence on digestive and absorptive mechanisms. Siddha system describes digestive capacity through the concept of Udal Agni (metabolic fire), with Tikshnaagni representing an intense, efficient digestive state. This manuscript explores the potential biochemical parallels between the Siddha concept of Tikshnaagni and modern understanding of gastrointestinal physiology, particularly in relation to Vitamin D bioavailability. We propose that enhanced enzymatic activity, optimal bile secretion, efficient micelle formation, and effective enterocyte transport-characteristics of optimal digestive function-may correlate with the functional attributes of Tikshnaagni. Integrating traditional concepts with biochemical evidence may offer novel insights into individualized nutrition and vitamin D deficiency management.