Vitamin D: benefits, dosage, contraindications

Vitamin D deficiency
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Vitamin D deficiency is common and underdiagnosed. The etiologies of hypovitaminosis D are multiple: decreased synthesis of cholecalciferol, low sun exposure, use of sunscreen creams, dark skin phototype, hepatic insufficiency, isoniazid treatment, genetic abnormality, renal insufficiency... The clinical manifestations of vitamin D deficiency are mainly musculoskeletal. Osteoporosis, osteomalacia in adults, and rickets in children are well-known bone manifestations. Unlike osteoporosis, osteomalacia is associated with generalized or localized bone pain (pain on pressure of the sternum or the tibial crest). A deficiency can also lead to proximal muscle weakness and may cause a waddling gait with lateral rocking movements (a "penguin gait"). In cases of insufficient intake, vitamin D is taken as weekly doses of 400 to 2000 IU (10 to 50 µg) for eight weeks. In confirmed nutritional rickets in children, in the absence of hypocalcemia, 25-OH vitamin D may be given at a dose of 1500 to 3000 IU per day for six to eight weeks, then 300 to 400 IU per day. In cases of hypocalcemia, the hypocalcemia should be treated for a few days before initiating vitamin D.

Posologie

Oral

400 - 2000 IU

8 - weeks

Adults

Bone health
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Vitamin D plays a major role in the regulation of blood calcium levels, blood phosphate levels, and bone homeostasis.rnrnEuropean health authorities (EFSA, European Food Safety Authority, and the European Commission) have concluded that dietary supplements containing vitamin D (calciferols) can claim to contribute to the intestinal absorption and utilization of calcium and phosphorus, to the maintenance of normal blood calcium levels, to normal bone growth in children, and to the maintenance of normal bone health.rnrn

Posologie

Orally

600 - 4000 IU

Adults

cholecalciferol

Hypoparathyroidism
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Oral administration of calcitriol is effective at increasing serum calcium concentrations in people with hypoparathyroidism or pseudohypoparathyroidism.rnrnIndeed, the relationship between vitamin D levels and those of parathyroid hormone (PTH) appears to be individually dependent on calcium intake. Dietary calcium influences PTH levels and, in turn, changes in PTH can alter the turnover of vitamin D metabolites. PTH acts indirectly by stimulating the 1-alpha-hydroxylation of vitamin D which, when activated to 1,25-dihydroxyvitamin D (1,25(OH)2D3), promotes intestinal calcium absorption.rnrnCalcium deficiency could therefore worsen vitamin D deficiency, whereas high intakes have, on the contrary, a vitamin D–sparing effect. rnrnIn cases of hypoparathyroidism, supplementation with vitamin D2 or vitamin D3 should be added when there is an associated deficiency or systematically at a dose of 400 to 800 IU/day.rnrn

Posologie

Orally

400 - 800 IU

Fractures
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The rate of bone fractures in older adults appears to be significantly reduced by vitamin D supplementation at 700 IU or more. Indeed, most studies use doses between 700 and 1000 IU, while lower doses do not seem to be effective.rnrnMoreover, concurrent calcium supplementation (and possibly vitamin K) appears to have a protective effect on bone.rnrn

Posologie

Oral

700 - 1000 IU

Seniors

Osteoporosis
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In cross-sectional studies, low 25(OH)D levels are associated with decreased bone mineral density (BMD), after adjustment for age, body mass index and calcium intake.rnrnThe National Osteoporosis Foundation (NOF) recommended in 2014 a daily vitamin D intake of 800 to 1,000 IU along with calcium to prevent osteoporosis in adults over 50. In patients with osteoporosis, the NOF recommends using vitamin D supplementation to maintain adequate vitamin D levels.rnrnThese recommendations are supported by clinical research showing that oral intake of vitamin D3 (cholecalciferol) with calcium supplements can reduce postmenopausal bone loss, may help prevent osteoporosis, and decrease the risk of fractures.rnrn

Posologie

Oral

800 - 1000 IU

Seniors

Psoriasis
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The topical application of vitamin D in the form of calcitriol or other vitamin D analogues appears effective for the treatment of plaque psoriasis in some patients, including the chronic form. Topical vitamin D or its analogues in combination with topical corticosteroids appears more effective than treatment with corticosteroids alone.

Posologie

Topically

calcitriol

Pregnancy
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Vitamin D, often associated with bone health, also plays a crucial role in the management of autoimmune diseases and allergies, as well as in maternal and fetal health during pregnancy. Preliminary research has shown that vitamin D supplementation may attenuate the severity of allergy symptoms such as allergic rhinitis, particularly when vitamin D levels are restored to an adequate threshold. Studies also suggest that insufficient vitamin D levels are associated with an increased risk of exacerbations and a greater need for medication in patients with asthma. Although clinical research findings are mixed, some meta-analyses have indicated that vitamin D supplementation may reduce the rate of asthma exacerbations in adults and children. Furthermore, vitamin D has been evaluated for its impact on other health outcomes during pregnancy, including preeclampsia, gestational diabetes, and markers of insulin resistance, potentially offering benefits in preventing and improving glycemic and lipid indices. Regarding child development, although some research suggests that increased vitamin D levels during pregnancy are associated with better anthropometric and neurodevelopmental outcomes, other studies have not shown a significant effect of vitamin D supplementation on children's neurological development. In summary, vitamin D supplementation during pregnancy offers significant benefits for maternal and fetal health, as confirmed by a meta-analysis including 30 trials and 7,033 women. Although the quality of evidence varies, vitamin D supplementation alone appears to reduce the risks of preeclampsia, gestational diabetes, and low birth weight, and may decrease the risk of severe postpartum hemorrhage.

Posologie

Oral administration

600 IU

Synergies

Asthma
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Analyses of clinical trials show that taking vitamin D for 3 months to 1 year reduces the number of asthma exacerbations by 31% to 36% in adults and children with asthma.rnrnVitamin D3 (cholecalciferol) was used at various dosages, either 100,000 IU followed by 4,000 IU per day for 7 months, or 120,000 IU every two months for 1 year.rnrn

Posologie

Oral administration

4,000 - 100,000 IU

7 - months

Premenstrual syndrome
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Increasing vitamin D intake appears to reduce the risk of developing premenstrual syndrome (PMS) and the severity of symptoms. Indeed, a clinical study shows that taking vitamin D at a dose of 400 IU/day in combination with 1000 mg/day of calcium for 10 days can reduce the severity of PMS symptoms.

Posologie

Oral administration

400 IU

10 days

Women

Synergies

Type 2 diabetes
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Observational research has shown that low vitamin D levels are associated with a higher risk of prediabetes, and that a diet rich in vitamin D is linked to a lower risk of developing diabetes. Moreover, in patients with vitamin D deficiency and prediabetes, vitamin D may improve beta-cell function, suggesting a reduction in disease progression.rnrnClinical research in adults with vitamin D deficiency shows that taking 50,000 IU of vitamin D per week for 3 months, then once monthly for 3 months, slightly improves insulin resistance and beta-cell function, but does not affect fasting and postprandial blood glucose compared with placebo. rnrnOral vitamin D may improve glycemic indices in some patients with type 2 diabetes, but clinical trial results remain conflicting. rnrn

Posologie

Oral

5000 IU

Respiratory infections
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Increased vitamin D levels during pregnancy have been associated with a lower incidence of respiratory infections in children. However, two meta-analyses of small clinical trials show a limited effect of prenatal vitamin D supplementation on the incidence of respiratory infections in infants or children (a 19% reduction in the risk of wheezing compared with the control group). In children, most research shows that vitamin D supplementation reduces the risk of respiratory infections. A meta-analysis of clinical trials conducted in children aged 1 to 16 years shows that taking vitamin D reduces the risk of suffering a respiratory infection compared with the control group. Daily or weekly doses of vitamin D appear to be more beneficial than single doses. Observational studies in adults have shown that low vitamin D levels are associated with worsened complications related to respiratory infections, and even with increased mortality from respiratory infections in adults aged 50 to 75 years. However, meta-analyses of prospective clinical trials in adults show that taking vitamin D supplements of 300 to 4,000 IU per day for 7 weeks to 5 years does not reduce the likelihood of developing a respiratory infection or serious respiratory complications, such as emergency department visits, hospitalization, and death, compared with placebo. By contrast, the largest single clinical trial, conducted in adults aged at least 60 years, shows that taking vitamin D3 (cholecalciferol) at 60,000 IU once a month for up to 5 years reduces the duration of overall and severe respiratory symptoms but does not reduce the incidence of respiratory illness, compared with placebo.

Posologie

Oral

4000 IU

Autoimmune diseases
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Vitamin D plays a crucial role in managing autoimmune diseases by influencing immune status through environmental, genetic, and epidemiological factors. Its insufficiency has been associated with an increased prevalence of autoimmune disorders, notably type 1 diabetes, multiple sclerosis, systemic lupus, and Crohn's disease. Studies in animal models and epidemiological observations suggest that vitamin D may reduce inflammation and improve T-cell function, offering protection against autoimmune diseases by regulating immune responses and decreasing inflammatory cytokines.

Posologie

Oral

400 - 2000 IU

Parkinson's disease
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A low serum level of vitamin D is correlated with an increased risk of Parkinson's disease and is furthermore associated with the severity of the pathological condition. rnrnIndeed, vitamin D can protect neurons from stressors, although a deficiency does not appear to inherently increase the risk of neuronal damage to cells associated with the disease.rnrnPreliminary research shows that taking 1200 IU/day of cholecalciferol (vitamin D3) for one year significantly slows disease progression in affected subjects.rnrn

Posologie

Orally

1200 IU

1 - years

Seniors

Cancer
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Epidemiological research has shown that a higher serum vitamin D level is associated with a decreased risk of mortality in patients with colorectal cancer. rnrnIndeed, in an analysis of studies assessing the association between serum vitamin D levels and colorectal cancer risk, people with serum vitamin D levels of 33 ng/mL or higher had a 50% lower risk of developing colorectal cancer compared with those with levels of 12 ng/mL or lower.rnrnHowever, it is unclear whether vitamin D supplementation improves survival in patients with colorectal cancer.rnrnSome research shows that a high calcium intake is associated with a reduced risk of adenoma recurrence and colorectal cancer among people whose vitamin D levels are above average.rnrnIn cases of colorectal cancer, vitamin D has been used at 8,000 IU per day during the first cycle of chemotherapy, then 4,000 IU per day for subsequent cycles.rnrnOn the other hand, some research has found that higher vitamin D intake is associated with a 17% reduction in breast cancer risk in pre- and perimenopausal women, but not in postmenopausal women.rnrn

Posologie

Oral

4,000 - 8,000 IU

Depression
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The role of vitamin D in the treatment of depression is unclear. Meta-analyses show that vitamin D supplementation does not improve depressive symptoms in general. However, some studies suggest that vitamin D may be beneficial in improving depressive symptoms in people with clinically significant symptoms and with an existing vitamin D deficiency prior to supplementation.rnrnVitamin D3 (cholecalciferol) has been administered as a single dose of 150,000 to 300,000 IU, or at daily and weekly doses ranging between 400 and 5,000 IU per day or 20,000 to 40,000 IU per week for 6 weeks to 2 years.rnrn

Posologie

Oral

400 - 5000 IU

2 - years

Multiple sclerosis
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The demographic study showed that long-term vitamin D supplementation in women reduces the risk of multiple sclerosis (MS) by up to 40%. The effect appears to be dose-dependent. Intake of at least 400 IU per day, mainly in the form of a multivitamin supplement, appears to have the greatest protective effect. Further research has found that higher levels of calcifediol (25-hydroxyvitamin D) are associated with a significantly lower risk of developing MS.rnrnVitamin D supplementation does not appear to have an effect on MS relapses. Indeed, meta-analyses show that vitamin D supplementation, whether low- or high-dose, does not affect MS relapse rate or the number of nerve lesions.rnrn

Posologie

Oral

400 IU

Systemic lupus erythematosus
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Clinical studies have shown that taking vitamin D3 (cholecalciferol) at a dose of 2000 IU per day or 50,000 IU per week appears to reduce anti-native DNA antibodies, a marker of disease activity, compared with placebo in patients with systemic lupus erythematosus.

Posologie

Orally

2000 IU

COVID-19
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The evidence for the role of vitamin D in preventing COVID-19 is conflicting. Although some observational research suggests that low vitamin D levels are associated with an increased risk of COVID-19, a large meta-analysis of observational studies found that vitamin D deficiency in adults was not associated with an increased risk of COVID-19 infection. However, 65% more people with severe disease had a vitamin D deficiency. In addition, vitamin D insufficiency, defined by blood levels below 30 ng/mL, was associated with more than an 80% increase in the risk of hospitalization or death from COVID-19. However, many of these studies did not account for patient age or other comorbidities. Some research has also examined an association between the use of vitamin D supplements and COVID-19 infection rates or disease severity. In the UK population, an observational study found that regular use of vitamin D supplements between 2006 and 2010 was associated with a 34% lower risk of COVID-19 infection. This result remained positive after adjusting for baseline health status and the use of other micronutrients. However, a high-quality prospective clinical trial conducted in patients hospitalized for moderate to severe COVID-19 shows that taking a single oral dose of 200,000 IU of vitamin D3 does not reduce length of hospital stay compared with placebo. In addition, it had no effect on in-hospital mortality, ICU admission, or the need for ventilation. The majority of patients in this study were vitamin D sufficient.

Posologie

Orally

400 - 1000 IU