Is vitamin d water or fat soluble
Pro Research Analysisby 
Searched over 200M research papers
Vitamin D: Solubility and Biological Functions
Fat-Soluble Nature of Vitamin D
Vitamin D is classified as a fat-soluble vitamin, meaning it dissolves in fats and oils but not in water. This characteristic is crucial for its absorption and storage in the body. Multiple studies confirm that vitamin D is fat-soluble and not water-soluble2 3 5 6 7.
Solubility in Various Solvents
Research has shown that vitamin D3, a common form of vitamin D, is practically insoluble in water. Its solubility in water is extremely low, with a mole fraction of 1.03 × 10⁻⁶1. In contrast, vitamin D3 is very soluble in organic solvents such as ethanol, isopropanol (IPA), ethyl acetate (EA), and various butanols1. This solubility profile underscores its classification as a fat-soluble vitamin.
Biological Functions and Importance
Vitamin D plays multiple roles in the body, including the regulation of calcium and phosphate levels, which are essential for bone health. It also has significant roles in brain and neurocognitive functions, and its deficiency has been linked to psychiatric disorders like depression2. Additionally, vitamin D is involved in immune modulation and has been associated with reduced risks of various diseases, including cardiovascular diseases, cancers, and autoimmune disorders3 6.
Vitamin D in Human Milk
There has been some debate about the presence of water-soluble forms of vitamin D in human milk. Earlier studies suggested the presence of water-soluble vitamin D sulfate in human milk, but these findings have been questioned and remain controversial4. The predominant consensus is that vitamin D in its active forms is fat-soluble.
Conclusion
In summary, vitamin D is a fat-soluble vitamin with minimal solubility in water but high solubility in various organic solvents. Its fat-soluble nature is essential for its biological functions, including bone health, immune modulation, and neurocognitive processes. Despite some historical debates, the overwhelming evidence supports its classification as a fat-soluble vitamin.
Sources and full results
Most relevant research papers on this topic
Solubility and thermodynamic function of vitamin D3 in different mono solvents
Vitamin D3 is practically insoluble in water, sparingly soluble in DMSO, PG, and PEG-400, and very soluble in ethanol, IPA, EA, 1-butanol, 2-butanol, and Transcutol®.
Efficacy of vitamin D in the treatment of depression: a systematic review and meta-analysis.
Vitamin D supplementation may be effective in treating depression, as it plays a role in various brain and neurocognitive processes and is linked to various psychiatric disorders.
Meta-AnalysisVitamin D: An Evidence-Based Review
Low vitamin D levels are associated with increased mortality, cancer, and autoimmune diseases, and may increase falls in the elderly.
Literature Review
Highly CitedWater-soluble vitamin D in human milk: a myth.
Human milk contains large quantities of water-soluble vitamin D sulfate, which has biologic activity in rats, but previous studies have questioned its presence and validity.
Role of vitamin D in female reproduction.
Vitamin D plays a crucial role in female reproduction, influencing ovarian reserve, steroidogenesis, infertility, and the outcomes of IVF, insulin resistance, hyperandrogenism, endometriosis, and polycystic ovary syndrome.
Highly CitedVitamin D and Infectious Diseases: Simple Bystander or Contributing Factor?
Vitamin D deficiency may contribute to increased incidence and severity of infectious diseases, and monitoring and supplementation may be beneficial in these settings.
Literature Review
Very Rigorous JournalHighly CitedMetabolic engineering for the production of fat-soluble vitamins: advances and perspectives
Metabolic engineering strategies show promise in producing fat-soluble vitamins through biotechnological routes, such as transgenic plants, microalgae, and microbial fermentation.
Overview of vitamin D and C requirements in fish and their influence on the skeletal system
Vitamin D and C are essential for maintaining calcium and phosphate homeostasis in fish, as well as regulating bone mineralization and skeletal integrity.
Highly CitedFat-soluble vitamins.
Fat-soluble vitamins, such as vitamin A, vitamin D, vitamin E, and vitamin K, have individual biochemical functions and differ from water-soluble vitamins in their binding to apoenzymes.
Vitamins and Minerals
Fat-soluble vitamins can be stored in the body, while water-soluble vitamins need to be taken daily as they are lost in urine.
Highly Cited