Vitamin D is a term referring to a type of steroid (derived from cholesterol) molecule found in the body and in food associated with a variety of biological mechanisms involved in maintaining life and health. There is more than one subtype of Vitamin D, but cholecalciferol, also known as Vitamin D3, tends to be most relevant to human physiology. Cholecalciferol is involved in the regulation of growth and development, cell functions, natural immunity and mineral absorption.
Deficiency in Vitamin D3 is linked to many diseases and conditions. Although human skin cells can synthesise the vitamin in response to sunlight exposure1
, some researchers conclude that a chronic lack of sunlight, experienced by many large regions of the Earth for extensive parts of the year, are responsible for the prevalence of many illnesses2
. Therefore, it is hypothesised that increased vitamin D intake, through diet or supplements, may reduce the risks of these disorders and conditions. Vitamin D is popularly associated with benefits to many areas of health and wellbeing, several of which are discussed below.
Vitamin D and Bone health
Bones are made up of specific matrices of the element calcium. Therefore, calcium is an important mineral or inorganic component of an individual’s diet. Vitamin D plays an essential role in absorbing calcium from the gut into the rest of the body, so that bone cells can take it up and continue to develop or maintain bone integrity3
. In addition, vitamin D may play a role in muscle cell growth and development, which also contributes to skeletal health4
Vitamin D deficiency can cause a disease in childhood, rickets, in which bones do not form properly, and may take on a 'bowed' appearance5
. Osteomalacia is the adult form of rickets, which may cause spinal abnormalities and chronic musculoskeletal pain. Children in countries at latitudes allowing for relatively high and consistent sunlight exposure may still develop rickets due to vitamin D-deficient diets5
. People with osteoporosis, a condition in which bone density decreases, and is strongly associated with post-menopausal women, may also benefit from maintaining optimal vitamin D levels through diet or supplements2
It can be difficult to separate the effects of vitamin D on bone health from those of calcium, as both are so intrinsically linked in bone formation6
. Many studies have found moderate benefits of vitamin D on bone health and density6
. A review of 7 trials including over 46,000 subjects on the effects of vitamin D and calcium co-supplementation found this did not affect the risk of hip fractures, but another two trials (with approximately 3800 subjects) showed that this co-administration reduced the incidence of hip fractures7
Vitamin D and Cardiovascular health
Optimal Vitamin D intake is often linked to cardiovascular health, as the vitamin contributes to the health of cells that make up the linings of artery walls8
. These cells are often at particular risk of damage in diabetic patients, which increases the risk of cardiovascular disorders in this population8
. A 12-week trial comparing vascular function in 50 diabetic patients receiving 5000 IU of vitamin D supplements daily with 50 receiving a placebo daily found no effect of supplementation on this or other biological markers of cardiovascular damage8
. A European study including 1006 adolescents demonstrated an association between low vitamin D levels and reduced cardiovascular fitness9
. In addition, obesity or high body fat is associated with vitamin D deficiency9
. (It appears from this study that reduced fitness and increased body fat are causative factors of reduced vitamin D, not the other way around.9
) A recent analysis of 9 trials (approximately 48,000 subjects) found no effect of vitamin D supplementation on heart attack or heart disease7
. Similar analysis of 8 trials (over 46,000 subjects) found no effect of this on the risk of stroke7
Vitamin D and the Immune system function
Vitamin D has been found to play a role in the control of the immune system and its cells10
. It is often linked to the prevention or treatment of autoimmune disorders11
. Deficiencies in the vitamin, or abnormalities in its receptor on immune cells, may play a role in disorders in which inflammation is a factor(also controlled by the immune system), such as diabetes, inflammatory bowel disease, and rheumatoid arthritis10
. In a study comparing patients with inflammatory bowel disease and healthy control subjects, reduced vitamin D was correlated with increased intestinal inflammation12
. A similar study comparing 181 people with rheumatoid arthritis with 186 controls showed that vitamin D levels were significantly lower in the arthritis patients. Disease activity (i.e. incidences of pain or other symptoms) was not associated with vitamin D deficiency, however13
A study of vitamin D-deficient diabetics randomised 118 patients to either 50000 IU vitamin D per week, 1000mg calcium a day, a combination of the two or placebo, for 8 weeks. Inflammatory biological markers (interleukin-6 and TNF-alpha) were significantly reduced for the calcium, vitamin D and combination groups compared to placebo14
. Therefore, supplementation in some immune system disorders may be beneficial, but more research into the efficacy of this may be necessary.
Vitamin D associated with Cognitive Functions
Neurological studies have found that the vitamin D receptor is found in many areas of the brain involved in cognition15
. Defects in the vitamin D receptor are also associated with Alzheimer's disease and Parkinson's disease15
. An analysis of 7 trials including just under 7,700 subjects indicated a significant association between mild cognitive impairment (a condition in which cognitive deficit is greater than the normal age-related changes but not severe enough to fulfil the criteria of dementia) and reduced vitamin D intake16
. Another review of 4 studies of Alzheimer's disease indicated that patients had reduced vitamin D concentrations in comparison to healthy controls17
. This indicates the need for placebo-controlled trials of the effects of supplementation on conditions in which cognitive faculties are affected.
Vitamin D and Health in Pregnancy
Vitamin D deficiency may impact on both the mother and foetus in the course of pregnancy. A review of 31 studies indicated its association with a higher risk of pre-eclampsia, low birth weight and diabetes during pregnancy18
Vitamin D and Longevity/Elder Health
Advancing age is associated with the decreased capacity of skin cells to produce a precursor of vitamin D, thus reducing the availability of cholecalciferol from skin19
. Therefore, supplementation is often recommended to combat the effects of potential bone and muscle loss, which may increase the risk of death or disability in the elderly4
. However, a review of 38 trials involving approximately 81,000 subjects on the effects of vitamin D supplementation on mortality was inconclusive7
- Holick MF. Sunlight, ultraviolet radiation, vitamin D and skin cancer: how much sunlight do we need? Advances in experimental medicine and biology.2014;810:1-16.
- Rizzoli R, Boonen S, Brandi ML, et al. Vitamin D supplementation in elderly or postmenopausal women: a 2013 update of the 2008 recommendations from the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO). Current medical research and opinion.2013;29(4):305-313.
- Schwalfenberg GK. The alkaline diet: is there evidence that an alkaline pH diet benefits health? Journal of environmental and public health.2012;2012:727630.
- Wagatsuma A, Sakuma K. Vitamin D Signaling in Myogenesis: Potential for Treatment of Sarcopenia. BioMed research international.2014;2014:121254.
- Pettifor JM. Nutritional rickets: deficiency of vitamin D, calcium, or both? The American journal of clinical nutrition.2004;80(6 Suppl):1725s-1729s.
- Cranney A, Horsley T, O'Donnell S, et al. Effectiveness and safety of vitamin D in relation to bone health. Evidence report/technology assessment.2007(158):1-235.
- Bolland MJ, Grey A, Gamble GD, Reid IR. The effect of vitamin D supplementation on skeletal, vascular, or cancer outcomes: a trial sequential meta-analysis. The Lancet Diabetes & Endocrinology.2014;2(4):307-320.
- Yiu YF, Yiu KH, Siu CW, et al. Randomized controlled trial of vitamin D supplement on endothelial function in patients with type 2 diabetes. Atherosclerosis.2013;227(1):140-146.
- Valtuena J, Gracia-Marco L, Huybrechts I, et al. Cardiorespiratory fitness in males, and upper limbs muscular strength in females, are positively related with 25-hydroxyvitamin D plasma concentrations in European adolescents: the HELENA study. QJM : monthly journal of the Association of Physicians.2013;106(9):809-821.
- Arnson Y, Amital H, Shoenfeld Y. Vitamin D and autoimmunity: new aetiological and therapeutic considerations. Annals of the rheumatic diseases.2007;66(9):1137-1142.
- Schwalfenberg GK. Solar radiation and vitamin D: mitigating environmental factors in autoimmune disease. Journal of environmental and public health.2012;2012:619381.
- Garg M, Rosella O, Lubel JS, Gibson PR. Association of circulating vitamin D concentrations with intestinal but not systemic inflammation in inflammatory bowel disease. Inflammatory bowel diseases.2013;19(12):2634-2643.
- Matsumoto Y, Sugioka Y, Tada M, et al. Relationships between serum 25-hydroxycalciferol, vitamin D intake and disease activity in patients with rheumatoid arthritis -TOMORROW study. Modern rheumatology / the Japan Rheumatism Association.2014:1-5.
- Tabesh M, Azadbakht L, Faghihimani E, Tabesh M, Esmaillzadeh A. Calcium-vitamin D co-supplementation influences circulating inflammatory biomarkers and adipocytokines in vitamin D insufficient diabetics: a randomized controlled clinical trial. The Journal of clinical endocrinology and metabolism.2014:jc20141977.
- Schlogl M, Holick MF. Vitamin D and neurocognitive function. Clinical interventions in aging.2014;9:559-568.
- Etgen T, Sander D, Bickel H, Sander K, Forstl H. Vitamin D deficiency, cognitive impairment and dementia: a systematic review and meta-analysis. Dementia and geriatric cognitive disorders.2012;33(5):297-305.
- Balion C, Griffith LE, Strifler L, et al. Vitamin D, cognition, and dementia: a systematic review and meta-analysis. Neurology.2012;79(13):1397-1405.
- Aghajafari F, Nagulesapillai T, Ronksley PE, Tough SC, O'Beirne M, Rabi DM. Association between maternal serum 25-hydroxyvitamin D level and pregnancy and neonatal outcomes: systematic review and meta-analysis of observational studies. BMJ (Clinical research ed.).2013;346:f1169.
- MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. The Journal of clinical investigation.1985;76(4):1536-1538.