vitamin d4

Vitamin D4, scientifically known as 22‑dihydroergocalciferol, is a form of vitamin D that belongs to the broader family of fat‑soluble secosteroids collectively referred to as vitamin D. While most public health guidance and dietary recommendations focus on the more common forms—vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol)—vitamin D4 has been identified in certain fungi and mushrooms, particularly those exposed to ultraviolet light. In biochemical nomenclature, vitamin D4 differs from D2 and D3 by modifications in the side chain of the molecule, but it retains the core secosteroid structure that allows it to be processed by the body into metabolites that participate in calcium regulation. In the body, vitamin D precursors such as D3, D2, and likely D4 undergo two hydroxylations: first in the liver to form 25‑hydroxyvitamin D (calcidiol), and then in the kidneys to form the hormonally active 1,25‑dihydroxyvitamin D (calcitriol). These active metabolites bind to the vitamin D receptor (VDR), a nuclear receptor found in many cell types which modulates gene expression. While the biological potency of vitamin D4 relative to D3 and D2 in humans is not as well established, research confirms its presence in the food supply and potential contribution to total vitamin D intake. The discovery of vitamin D4 in mushrooms was documented in chromatographic analyses where UV spectra consistent with vitamin D4 were resolved, indicating that ergosta‑5,7‑dienol can be converted to vitamin D4 in response to UV exposure. Compared to other forms, vitamin D4 is less abundant and less studied in clinical settings, but it functions within the same metabolic pathways that regulate bone health, calcium homeostasis, and other physiological processes influenced by vitamin D. Understanding its occurrence expands our knowledge of dietary vitamin D beyond traditional D2 and D3 forms and underscores the diversity of vitamin D vitamers in foods such as fungi.

Like other forms of vitamin D, including D3 and D2, vitamin D4 contributes to the systemic pool of vitamin D that influences multiple aspects of human health. The principal role of vitamin D, regardless of its specific form, is to facilitate the absorption of calcium and phosphorus from the intestine, which is essential for the maintenance of healthy bones and teeth. Without adequate vitamin D, the body cannot efficiently absorb these minerals, leading to compromised bone mineralization, which over time results in conditions such as rickets in children and osteomalacia in adults. The active metabolite of vitamin D interacts with the vitamin D receptor (VDR) in the intestinal epithelium to upregulate the expression of calcium‑binding proteins, enhancing calcium uptake. Beyond bone health, vitamin D influences immune function by modulating both innate and adaptive immune responses. Immune cells express the vitamin D receptor, and evidence suggests vitamin D plays a role in the regulation of cytokine production and the activity of T cells and macrophages. While most clinical research has focused on vitamin D3, mechanistic pathways involving vitamin D receptor signaling likely extend to metabolites derived from vitamin D4. Observational studies have shown correlations between adequate vitamin D status and reduced risk of certain infections and autoimmune diseases, though definitive causal evidence remains under investigation. Vitamin D also influences muscle function; deficiency is associated with muscle weakness and increased risk of falls in older adults. Meta‑analyses of supplementation trials focusing on vitamin D (primarily D3) demonstrate modest improvements in muscle performance and reduction in fall risk among older adults with low baseline levels, supporting a role for vitamin D in neuromuscular health. Furthermore, vitamin D participates in regulating cellular proliferation and differentiation, and research has explored its potential links to chronic diseases such as type 2 diabetes and certain cancers. While supplementation trials have yielded mixed results, high serum levels of 25‑hydroxyvitamin D are consistently associated with lower incidence of colorectal cancer and improved markers of glycemic control in observational studies. The specific contribution of vitamin D4 to these outcomes is not well delineated due to limited research focused on this form, but it is reasonable to infer that vitamin D4 contributes to the total vitamin D pool that underpins these physiological effects. Therefore, ensuring sufficient intake of all forms of vitamin D, including vitamin D4 where present in foods like UV‑exposed mushrooms, supports these broad health functions.

Official dietary reference intakes for vitamin D do not differentiate between vitamin D4, D2, and D3; rather, they define recommended intake levels for total vitamin D activity. In the United States and Canada, the Food and Nutrition Board has established Recommended Dietary Allowances (RDAs) for vitamin D expressed as micrograms (mcg) or International Units (IU). For infants 0–12 months, the Adequate Intake (AI) is set at 400 IU (10 mcg) per day. For children and adults up to age 70, the RDA is 600 IU (15 mcg) per day, increasing to 800 IU (20 mcg) per day for adults over 70 years to account for decreased skin synthesis and other age‑related factors. Pregnant and lactating women are also advised to meet the 600 IU (15 mcg) RDA. The tolerable upper intake level (UL) for adults is set at 4,000 IU (100 mcg) per day, beyond which the risk of adverse effects such as hypercalcemia increases. These recommendations assume minimal sun exposure, recognizing that ultraviolet B radiation from sunlight contributes significantly to vitamin D status by enabling skin synthesis of precursors that are converted to active metabolites in the body. Factors influencing individual needs include geographic location, skin pigmentation, age, season, use of sunscreen, time spent outdoors, body weight, and health status. People with darker skin may require more sun exposure to achieve the same vitamin D synthesis as those with lighter skin due to higher melanin levels that reduce UVB penetration. Older adults have lower cutaneous synthesis capacity, making dietary and supplementary sources more critical for meeting vitamin D needs. While vitamin D4 specifically is not quantified separately in dietary guidance, it adds to the total vitamin D activity derived from the diet, complementing contributions from vitamin D2 and D3. Therefore, meeting recommended intakes of vitamin D through a combination of sunlight exposure, diet, and supplementation ensures adequate overall vitamin D status.

Deficiency of vitamin D, including contributions from vitamin D4, manifests as insufficient total vitamin D activity in the body. Clinical signs and symptoms stem from impaired calcium and phosphorus homeostasis and can vary in severity. In infants and young children, severe deficiency leads to rickets, characterized by soft, weak bones, bowed legs, delayed growth, and skeletal deformities. In adults, deficiency presents as osteomalacia, with symptoms including bone pain, muscle weakness, and increased susceptibility to fractures. Subtle deficiency may go unnoticed for years but can contribute to chronic musculoskeletal pain and increased risk of falls, particularly in older adults. Laboratory assessment of vitamin D status is typically based on measuring serum 25‑hydroxyvitamin D [25(OH)D], which reflects total vitamin D from sun exposure, diet, and supplements. While optimal ranges are debated, public health organizations often consider levels below 30 nmol/L (12 ng/mL) as deficient, with levels of 50 nmol/L (20 ng/mL) or higher considered adequate for bone and overall health. Symptoms such as muscle aches, fatigue, depression, and impaired wound healing have been linked to low serum 25(OH)D levels, though these associations are not specific to a single vitamin D form. Populations at increased risk of deficiency include individuals with limited sun exposure due to lifestyle or geographic location, those with malabsorption disorders that impair fat‑soluble vitamin uptake, older adults with decreased cutaneous synthesis capacity, and people with darker skin pigmentation requiring more UV exposure to generate equivalent vitamin D precursors. Prevalence studies indicate that a significant proportion of the population in higher latitudes has circulating 25(OH)D levels below recommended thresholds during winter months, underscoring the public health relevance of ensuring adequate vitamin D status through diet and supplementation where appropriate.

Although vitamin D4 itself is found in relatively few foods compared to other forms, it contributes to the total vitamin D activity when present. The richest sources of vitamin D activity are typically foods that contain significant amounts of vitamin D3 or D2, and some data indicate that UV‑exposed mushrooms contain measurable amounts of vitamin D4. In a chromatographic analysis of mushroom samples, peaks consistent with vitamin D4 were observed, indicating its presence alongside vitamin D2 in fungi exposed to ultraviolet light. Mushrooms exposed to UV light produce vitamin D2 and likely D4 from sterol precursors such as ergosta‑5,7‑dienol. Thus, UV‑treated mushrooms represent a unique source of vitamin D4 in the diet. However, USDA food composition databases generally aggregate vitamin D2 and D3 content and do not separately quantify vitamin D4, limiting precise nutrient profiling of this form. Nonetheless, for practical dietary planning, foods high in total vitamin D activity are recommended. These include fatty fish like salmon, mackerel, sardines, and trout, which provide substantial vitamin D3; fortified foods such as milk, plant milks, breakfast cereals, and juices; egg yolks; and cod liver oil. UV‑exposed mushrooms can be an important source of vitamin D2 and potentially vitamin D4, particularly for individuals following vegetarian or vegan diets. A broad variety of foods contributing vitamin D activity include salmon (both wild and farmed), canned tuna, fortified milk and plant milks, fortified breakfast cereals, fortified orange juice, eggs, and mushrooms exposed to UV light. The specific contribution of vitamin D4 in these foods is minor relative to D3 and D2 but adds to cumulative intake. Including a diverse array of vitamin D‑rich foods helps ensure adequate intake and supports bone health and other physiological processes dependent on vitamin D.

Common Forms: Vitamin D3 (cholecalciferol), Vitamin D2 (ergocalciferol)

Typical Doses: 600–2000 IU daily depending on needs

When to Take: With meals containing fat

Best Form: Vitamin D3

⚠️ Interactions: Orlistat may reduce absorption, Cholestyramine may reduce absorption