Addressing Vitamin D Deficiency in the Wound Care Clinic

The knowledge that most tissues and cells in the human body have the vitamin D receptor (VDR) and that several possess the enzymatic machinery to burn the major circulating form of vitamin D (calcidiol/25-hydroxyvitamin D) to the active form (calcitriol/1,25-dihydroxyvitamin D) has provided insight into the function of this vitamin. Today, more than one century after three Nobel prizes were awarded for its discovery, we have clear evidence that this so-called vitamin is in fact a pleiotropic steroid hormone similar to other steroid hormones. Its classification still greatly affects our perception about its biological role. The active form, now known as the “D hormone,” is a pleiotropic steroid hormone that has multiple biological affects and is integral to the regulation of calcium homeostasis and bone turnover, as well as having antiproliferative, prodifferentiation, antibacterial, immunomodulatory, and anti-inflammatory properties within the body in various cells and tissues. Cholecalciferol (Vitamin D₃) should be considered a nutritional substrate that must be ingested or synthesized in sufficient amounts for further synthesis of the important regulatory steroid hormone (D hormone), especially in patients living with rheumatic diseases. Vitamin D insufficiency or deficiency has been shown to be a pandemic and associated with numerous chronic inflammatory and malignant diseases, as well as an increased risk of mortality. Of great interest is the role vitamin D can play in decreasing the risk of many chronic illnesses including common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease. When the skin is injured, a higher amount of vitamin D intake will enhance healing and better outcomes. Additionally, vitamin D promotes the creation of cathelicidin, an antimicrobial peptide the immune system uses to fight off wound infections. 

SOURCES OF METABOLIZED VITAMIN D

Humans absorb vitamin D from exposure to sunlight, their dietary intake, and from dietary supplements. The “D” represents D₂ or D₃.  Vitamin D₂ is manufactured through the ultraviolet irradiation of ergosterol from yeast and vitamin D₃ for the ultraviolet irradiation of 7-dehydrocholesterol from lanolin. Both are used in over-the-counter supplements, but the form available by prescription in the United States is D₂. A diet high in oily fish prevents vitamin D deficiency. Solar ultraviolet B (UVB) radiation (wavelength 290; 2,315 mm) penetrates the skin and converts 7-dehydrocholesterol (a zoosterol that functions in the serum as a cholesterol precursor) to previtamin D₃, which is rapidly converted to vitamin D₃. Because any excess previtamin D₃ or vitamin D₃ is destroyed by sunlight, excessive exposure to sunlight does not cause vitamin D intoxication. Few foods naturally contain or are fortified with vitamin D. 

Vitamin D from the skin and diet is metabolized in the liver to calcifediol, which is used to determine a patient’s vitamin D status (calcifediol is metabolized in the kidneys by the enzyme calcifediol-1-alpha-hydroxylase [cytochrome P450 protein CYP27B1] to its active form calcitriol). The renal production of calcitriol is tightly regulated by plasma parathyroid hormone levels and serum calcium and phosphorus levels. Fibroblast growth factor 23, secreted from the bone, causes the cilium-phosphate co-transporter to be internalized by the cells of the kidney and small intestine and suppresses calcitriol synthesis. The efficiency of the absorption of renal calcium and of additional calcium phosphorus is increased in the presence of calcitriol. It also induces the expression of the enzyme calcitriol-24-hydroxylase (CYP24), which metabolizes both calcifediol and calcitriol into biologically inactive, water-soluble, calcitroic acid.

VITAMIN D HORMONE BIOLOGICAL ACTIVITY

For many years, it was believed the regulation of calcium homeostasis in the body with a positive influence on bone turnover were the only crucial roles for this hormone, and thus why it was considered to be a vitamin critical for bone health. This tenet remains correct, but it’s now also understood that all monocyte-macrophage derived cells, including those present in many tissues and various epithelia, are able to express CYP27B1 and to synthesis calcitriol locally. Synthesized D hormone can act on cells, in the tissues, and in an autocrine or paracrine manner; the synthesized D hormone calcitriol serves as a connection between extracellular stimuli and genomic response of the cells. It’s recognized the 1-alpha-hydroxylase calcidiol has high infinity by VDR due to the presence of an hydroxyl group at the 1-alpha position. The VDR shows its expression in tissues with high metabolic activity (such as kidneys, bone, and gut), but has low to moderate expression in nearly all other human tissues. VDR, when bound to hormone, heterodimerizes with the retinoic acid-X-receptor. This complex binds to the vitamin D responsive element acting as a transcriptional to enhance or repress gene transcription. It’s estimated that at least 200 tissues and as many as 2,000 genes are directly or indirectly controlled by this transcriptional complex. Only high doses of D hormone can induce genetic effects, including immunomodulatory actions, while physiological actions have to be mediated in the genetic and epigenetic regulatory actions of the VDR transcriptional complex. The VDR protein has been detected both in the cytosol (associated with sarcoplasmic reticulum calcium [CA2⁺ ATPase]) and in plasma membranes. This ubiquitous presence of the VDR protein may explain some of the rapid nongenomic actions of calcitriol, such as calcium uptake, that are related to calcium homeostasis and bone mineralization. Signaling pathways of all steroid hormones (glucocorticoid, sex hormones) occur through cellular and nuclear hormone receptors. All of these hormones influence bone formation and immune regulation. Steroid nuclear receptors, when bound to their agonist hormone under control of co-regulators, catalyze or mediate chromatin remodeling, epigenetic modification, receptor recycling, and, ultimately, gene expression.

Gene regulation appears to be modulated by dual modifications of histone acetylation and DNA methylation. The calcitriol hormone has been shown to be a potent genetic and epigenetic regulator. This could explain the possible pathogenic role of low vitamin D status in immune-mediated diseases. Using this same signaling pattern of calcitriol, which is locally produced in the tissues, exerts its effects on several immune cells, including macrophages, dendritic cells, and T and B cells.  Macrophages and dendritic cells constituently express VDR, whereas VDR expression in K cells is upregulated after activation. In macrophages and monocytes, calcitriol positively influences its own effects by increasing expression of VDR in CYP27B1. Toll-like receptor-mediated signals can also increase the expression of VDR. The calcitriol hormone also induces monocyte proliferation and production of interleukin-1 (IL-1) and cathelicidin (a powerful antimicrobial peptide) by macrophages, thereby contributing to innate immune response. The calcitriol hormone decreases dendritic cell maturation, inhibiting upregulation of the expression of major histocompatibility complex class II and cluster of differentiation (CD) 48, 80, and 86. In addition, it decreases IL-12 production of dendritic cells and induced production of IL-10. In T cells, calcitriol decreases the production of IL-2, IL-17, and gamma interferon, as well as attenuating the cytotoxic activity and proliferation of CD4⁺ and CD8⁺ T cells. The calcitriol hormone may also promote the development of scurfin, a protein involved in immune system responses. Finally, calcitriol blocks B-cell proliferation, plasma cell differentiation, and immunoglobulin production. It’s clear the D hormone exerts its effects on many crucial, important, immunoregulatory proteins and cells. Some are recognized as possible causative immune factors for the development of chronic inflammatory diseases; some are recognized as possible causative immune factors for the development of these arthrities. Due to the D hormone’s apparent capability to induce tolerogenic immune response, improve impaired T- and B-cell function, and enhance immunity response, deficiency or insufficiency of D hormone may well have causative risk factors in several chronic inflammatory diseases.

OPTIMAL HORMONE LEVELS 

The best method to determine a person’s vitamin D status is to measure the circulating level of calcifediol. Serum levels of calcitriol are often normal or even elevated in both children and adults who are vitamin D deficient due to its short half-life and tight physiologic control by parathyroid hormone, which can increase renal production of calcitriol by stimulating 1-alpha-hydroxylase activity. The vitamin D hormonal form is synthesized and accumulated to a large degree in the tissues, but it cannot be measured there. For a long time, there has been no consensus on the optimal concentrations of serum 25 (OHD). Most authors have used the cutoff values of 10-15 ng/mL to define vitamin D deficiency. In 2010, the Institute of Medicine (IOM) concluded vitamin D deficiency should be defined as a 25 OHD level of < 20 ng/mL for children and adults. 

According to the Endocrine Society, vitamin D deficiency is now defined as a 25 OHD < 25 ng/mL, vitamin D insufficiency is 21-29 ng/mL, and vitamin D sufficiency is > 30 ng/mL for both children and adults. The society also suggests maintenance of a 25 OHD level of 40-60 ng/mL as an ideal and up to 100 ng/mL as safe. The supplementation of 1,000 international units (IUs) of cholecalciferol per day increases the 25 OHD level by 7-10 ng/mL, and it’s believed 100 IU can increase 25 OHD levels by as much as 2-3 ng/mL when serum 25 OHD is < 15 ng/mL in adults. With the use of such definitions, it’s estimated 1 billion people worldwide live with vitamin D deficiency or insufficiency. According to several studies, 40-100% of U.S. and European elderly adults still living in the community (not in long-term care) are deficient in vitamin D. More than 50% of postmenopausal women taking medications for osteoporosis had suboptimal levels of calcifediol  < 30 ng/mL.

CALCIUM, PHOSPHORUS, & BONE METABOLISM

With vitamin D, only 10-15% of bacteria calcium and about 50% of phosphorus are absorbed. The interaction of calcitriol with the VDR increases the efficiency of intestinal calcium absorption to 30-40% and phosphorus absorption to approximately 80%. In one study, serum levels of calcidiol were directly related to bone mineral density in white, black, and Mexican-American adults, with a maximum density achieved when the calcidiol level reached ≥ 40 ng/mL.  When the level was ≤ 30 ng/mL there was significant decrease in intestinal calcium absorption that was associated with increased parathyroid hormone. Parathyroid hormone enhances the tubular reabsorption of calcium and stimulates the kidneys to calcitriol. Parathyroid hormone also activates osteoblasts that stimulate the transformation of preosteoclast into mature osteoclasts. Osteoclasts dissolve the mineralized collagen matrix in bone, causing osteopenia and osteoporosis while increasing the risk of fracture. The deficiencies of calcium and vitamin D in uterine and childhood may prevent the maximum deposition of calcium in the skeleton. As vitamin D deficiency progresses, the parathyroid glands are maximally stimulated, causing secondary hyperparathyroidism.

Hypomagnesemia blunts this response, meaning the parathyroid hormone levels are often normal when Calcidiol levels fall < 20 ng/mL. Parathyroid hormone increases the metabolism of calcidiol to calcitriol, which further exacerbates vitamin D deficiency. Parathyroid hormone also causes phosphaturia, resulting in a low-normal or low-serum phosphorus level. Without an adequate calcium-phosphorus product, mineralization of the collagen matrix is diminished, leading to classic signs of rickets in children and osteomalacia in adults. Whereas osteoporosis is associated with bone pain, osteomalacia has been associated with isolated or generalized bone pain. The cause is thought to be hydration of the demineralized gelatin matrix beneath the periosteum; the hydrated matrix pushes outward on the periosteum, causing throbbing, aching pain. Osteomalacia can often be diagnosed by using moderate force to press the thumb on the sternum or anterior tibia, which can elicit bone pain. One study shows 93% of people ages 65 years or older admitted to a hospital emergency department with muscle aches and bone pain, and who had a wide variety of diagnoses including fibromyalgia, chronic fatigue syndrome, and depression, were deficient in vitamin D. 

MUSCLE STRENGTH & FALLS

Vitamin D deficiency causes muscle weakness. Skeletal muscles have a VDR and may require vitamin D for maximal function. Performance, speed, and proximal muscle strength are markedly improved when calcidiol is increased from 4 to 16 ng/mL and continue to improve as levels increase to > 40 ng/mL. One meta-analysis of randomized, controlled trials (with a total of 1,237 subjects) revealed increased vitamin D intake reduced the risk of falls by 22% as compared with only calcium or placebo. The same meta-analysis exam of the frequency of falls suggests 400 IU of vitamin D₃/day was not effective in preventing falls, whereas 800 IU of vitamin D₃/day plus calcium reduced the risks of falls. In a randomized, controlled trial conducted over five months, nursing home residents receiving 800 IU of vitamin B₂/day plus calcium had a 72% reduction in the risk of falls as compared with the placebo group.

NONSKELETAL ACTIONS OF VITAMIN D

Brain, prostate, breast, and colon tissues, among others (as well as immune cells), have a VDR and respond to calcitriol. Directly or indirectly, calcitriol controls more than 200 genes, including those responsible for the regulation of safe proliferation, differentiation, apoptosis, and angiogenesis. It decreases cellular proliferation of both normal cells and cancer cells and induces their terminal differentiation. Calcitriol is also a potent immunomodulator. Monocytes and macrophages exposed to a lipopolysaccharide or to mycobacterium tuberculosis help regulate the VDR gene in the calcifediol-1-alpha-hydroxylase gene. Increased production of calcitriol D₃ results in synthesis of cathelicidin, a peptide capable of destroying mycobacterium tuberculosis as well as other infectious agents. When serum levels of calcifediol fall < 20 ng/mL, the monocyte or macrophage is prevented from initiating this innate immune response, which explains why black Americans, who are often vitamin D deficient, are more prone to contracting tuberculosis than whites and tend to have a more aggressive form of the disease. Calcitriol inhibits renin synthesis, increases insulin production, and increases myocardial contractility.

CHRONIC DISEASES

Cancer

People living in higher latitudes are at increased risk for Hodgkin’s lymphoma as well as colon, pancreatic, prostate, ovarian, breast, and other cancers. These individuals are also more likely to die from these cancers as compared to those living in environments at lower latitudes. Perspective and retrospective epidemiologic studies indicate levels of calcifediol < 20 ng/mL are associated with a 30-50% increased risk of colon, prostate, and breast cancer incidence, along with higher mortality from these cancers. An analysis from the Nurses Health Study Cohort (32,826 subjects) shows the odds for colorectal cancer are inversely associated with the medium serum levels of calcifediol.

Participants in a women’s health initiative who at baseline had a calcifediol concentration of < 12 ng/mL had a 253% increase in the risk of colorectal cancer over a follow-up period of eight years. Children and young adults exposed to the most sunlight had a 40% reduced risk of non-Hodgkin’s lymphoma, but no reduced risk of death from malignant melanoma once it develops, as compared with those who had the least exposure to sunlight. The point here is that since the kidneys tightly regulate the production of calcitriol, serum levels do not rise in response to increased exposure to sunlight or increased intake of vitamin D. 

Furthermore, in a vitamin D insufficient state, calcitriol levels are often normal or even elevated.  The likely explanation is that colon, prostate, breast, and other tissues express calcifediol-1-alpha-hydroxylase and produce calcitriol locally to control genes that help to prevent cancer by keeping cellulitic proliferation and differentiation in check. It’s suggested that if a cell becomes malignant, calcitriol can induce apoptosis and prevent angiogenesis, thereby reducing the potential for the malignant cell to survive. Once calcitriol completes these tasks, it initiates its own destruction by stimulating the CYP24 gene to produce the inactive calcitroic acid. This guarantees calcitriol does not enter the circulation to influence calcium metabolism. This is a plausible explanation for why increased sun exposure and higher circulating levels of calcifediol are associated with a decreased risk of deadly cancers.

Autoimmune, Osteoarthritis, & Diabetes

Living at higher latitudes also increases the risk of type 1 diabetes, multiple sclerosis, and Crohn’s disease. Among white men and women, the risk of multiple sclerosis decreases by 41% for every increase of 20 ng/mL in calcifediol > approximately 24 ng/mL. Women who ingested more than 400 IUs/day of vitamin D had a 42% reduced risk of developing multiple sclerosis. Similar observations have been made for rheumatoid arthritis and osteoarthritis. Several studies have suggested vitamin D supplementation in children reduces the risk of type 1 diabetes. Increasing vitamin D intake during pregnancy reduces the development of islet autoantibodies in the child.

In one study, 10,366 children in Finland who were given 2,000 IU/day of vitamin D₃ during their first year of life and were followed for 31 years, the risk of type 1 diabetes was reduced by approximately 80%.  Among children with vitamin D deficiency, the risk was increased by approximately 200%. In another study, vitamin D deficiency increased insulin resistance, decreased insulin production, and was associated with metabolic syndrome.  

Cardiovascular Disease

Living at higher latitudes also increases the risk for hypertension and cardiovascular disease. A study of patients living with hypertension who were exposed to UVB radiation three times per week for three months saw calcifediol levels increased by approximately 180% and blood pressure became normal (both systolic and diastolic; blood pressure reduced by 6 mm of mercury). Vitamin D deficiency is associated with congestive heart failure and blood levels of inflammatory factors, including C-reactive protein and IL-10.

CAUSES OF VITAMIN D DEFICIENCY

Reduced skin synthesis and absorption of vitamin D, as well as acquired and inheritable disorders of vitamin D metabolism and its responsiveness, are among the causes of vitamin D deficiency. Sunscreen use, deficiencies in skin pigment, aging, season, latitude, and time of day also influence our ability to produce and absorb vitamin D. 

Patients who are prescribed anticonvulsants, glucocorticoids, AIDS treatment, and antirejection medication could have increased metabolism. Patients breastfed by women living with poor vitamin D can experience increased risk of vitamin D deficiency when breast milk is the sole source of nutrition. Other examples could be decreased synthesis of calcifediol that is seen in patients living with liver failure, which then causes malabsorption of vitamin D. However, production of calcifediol is possible. There could also be increased urinary loss of calcifediol, as in the case of nephrotic syndrome, which leads to substantial loss of calcifediol bound to vitamin D-binding protein within urine. Also, there may be decreased synthesis of calcitriol that is seen in chronic kidney disease (CKD). Stages II and III, as well as hyperphosphatemia, increases fibroblast growth factor 23, which decreases calcifediol-1-alpha-hydroxylase activity. Stages IV and V — when glomerular filtration rate is < 30 and inability to produce adequate amounts of calcitriol — will result in decreased fractional excretion of phosphorus and decreased serum levels of calcitriol as well as cause hypercalcemia secondary to hyperparathyroidism and renal bone disease.

VITAMIN D REQUIREMENTS & TREATMENT STRATEGIES

Recommendations for adequate daily intake of vitamin D from the IOM are 200 IU for children and adults up to 50 years old, 400 IU for adults ages 51-70, and 600 IU for adults aged 71 years or older. However, most experts agree that without adequate sun exposure, children and adults require approximately 800-1,000 IU/day. 

Children experiencing vitamin D deficiency should be aggressively treated to prevent rickets. Since vitamin D₂ is approximately 30% as effective as vitamin D₃ in maintaining serum calcifediol levels, up to three times as much vitamin D₂ may be required to maintain sufficient levels. A cost-effective method of correcting vitamin D deficiency and maintaining adequate levels is to prescribe patients a 50,000-IU capsule of vitamin D₂ once per week for eight weeks followed by 50,000 IU of vitamin D₂ every 2-4 weeks thereafter. Alternatively, either 1,000 IU of vitamin D₃ or 3,000 IU of vitamin D₂ per day is effective.  

STRATEGIES FOR CKD 

With any stage of CKD, calcifediol should be measured every three months and the levels should be maintained at ≥ 30 ng/mL, as recommended by the National Kidney Foundation.^® It’s a misconception to assume patients taking an active vitamin D analog have sufficient vitamin D.  Levels of calcifediol are inversely associated with parathyroid hormone levels, regardless of the degree of chronic renal failure. 

The parathyroid gland converts calcifediol to calcitriol, which directly inhibits parathyroid hormone expression. Patients living with stage IV or stage V CKD and an estimated glomerular filtration rate of < 30 mL/minute, as well as those on chronic dialysis, are unable to make enough calcifediol and need to take calcitriol D₃or one of its less calcemic analogs to maintain calcium metabolism and to decrease parathyroid hormone levels as well as the risk of renal bone disease.

SUNLIGHT & ARTIFICAL UVB RADIATION

Sensible sun exposure can provide an adequate amount of vitamin D₃, which is stored in body fat and released during the winter when it cannot be produced. Exposure of arms and legs for 5-30 minutes, depending on time of day, season, latitude, and skin pigmentation (between the hours of 10 a.m. and 3 p.m.) twice per week is often adequate. Exposure to one minimal erythemal dose while wearing only a bathing suit is equivalent to ingesting approximately 20,000 IU of vitamin D₂.  The skin has a great capacity to make vitamin D₃ even in the elderly, to reduce the risk of fracture. 

VITAMIN D INTOXICATION

Vitamin intoxication is extremely rare, but can be caused by inadvertent or intentional ingestion of excessively high doses. Doses > 50,000 IU/day raise levels of calcifediol to > 150 ng/mL and are associated with hypercalcemia and hyperphosphoremia. However, doses of 10,000 IU/day of vitamin D₃ for up to five months do not cause toxicity.  Patients living with chronic granulomatous disorders (eg, sarcoidosis) are more sensitive to serum calcifediol > 30 ng/mL because of macrophage production of calcitriol, which causes hypercalciuria and hypercalcemia. In these patients, calcifediol levels need to be maintained at approximately 20-30 ng/mL to prevent vitamin D deficiency and secondary hyperparathyroidism.

Matthew Regulski is director of the Wound Institute of Ocean County, Toms River, NJ, and partner at the Ocean County Foot & Ankle Surgical Associates P.C., Toms River.