Vitamins play a crucial role in the human body’s metabolism and these exotic molecules are essential for the proper functioning of cells in the body. Vitamins are organic chemicals that must be obtained from dietary sources, as the body does not make vitamins. Theory has it that somewhere along the process of evolution, our bodies have lost the ability to make vitamins, so instead we need to obtain them from our diet.
Of course there would be one exception to prove the rule, and in the case of vitamins, it is Vitamin D, which our cells in the skin can make if there is enough sunlight. No wonder it is referred to as the “sunshine vitamin”.
The epidermal layer of the skin synthesizes vitamin D when exposed to ultraviolet B rays (UVB) in sunlight. A form of vitamin D called cholecalciferol is synthesized from a derivative of the steroid cholesterol in the skin. The liver converts cholecalciferol to calcidiol, the storage form of vitamin D, which is then converted in the kidneys to calcitriol, which is the active, steroid-hormone form of vitamin D.
Very little vitamin D is available from dietary sources. Small amounts of vitamin D are found in food such as egg yolks and oily fish, but not in sufficient quantities for the body’s needs.
Vitamin D is a fat-soluble vitamin that the body can store for a long time and one of its important functions is to maintain normal blood levels of calcium. It acts as facilitator for the absorption of calcium in the small intestine, which is essential to form and maintain strong bones. The body absorbs about 30% to 40% of dietary calcium with normal levels of vitamin D, but only about 10% to 15% when vitamin D levels are low.
Apart from its role in the absorption of calcium, vitamin D receptors are found in in almost every cell in the body. It turns genes on and off, leading to changes in cells. It’s multiple functions in the body include playing roles in immune function, cell proliferation, differentiation, and apoptosis.
Vitamin D deficiency:
Vitamin D deficiency, also referred to as hypovitaminosis D, is a common vitamin deficiency, which means vitamin D levels are below normal and your body is not getting enough vitamin D to stay healthy. This happens when intakes are lower over time than recommended levels. It is a common occurrence when people have inadequate exposure to sunlight with ultraviolet B (UVB) rays, or inadequate nutritional intake of vitamin D, or the body isn’t properly absorbing or using vitamin D. Interestingly, UVB rays do not penetrate glass, which means exposure to sunlight through glass does not produce vitamin D in the skin.
While there is a large interindividual variation in the vitamin D synthetic ability of the skin, UVB sunlight exposure is also affected by indoor working hours, season of the year, style of clothing, the use of sunscreen, and latitude. Except during the summer months, the skin makes very little vitamin D from the sun at latitudes above 37 degrees north or 37 degrees south of the equator.
Effects of vitamin D deficiency:
Vitamin D deficiency means a decline in calcium and phosphorous absorption in the intestines. Low calcium levels in the blood can lead to a loss of bone density and cause bones to become thin, brittle, or misshapen. Severe vitamin D deficiency can lead to other related health conditions, such as muscle weakness or cramps, worsening of osteomalacia (weak bones) and osteoporosis in adults, and rickets in children.
Apart from its effects on calcium and bone homeostasis, there is much more to vitamin D than meets the eye, for instance by acting as a master conductor in the symphony of our genes.
Vitamin D is known to regulate a variety of genes or gene products in different genetic circuits. Vitamin D regulates gene expression by binding to specific receptors in the nucleus of cells, where it initiates a series of molecular events that activate or suppress target genes. It follows that vitamin D plays a vital role in gene regulation in various body systems, such as influencing genes that are involved in immune function, inflammation, cell growth, and cell differentiation.
While optimal gene expression helps to ensure that the cells in the body function harmoniously, disruptions in gene regulation, such as vitamin D deficiency, may contribute to various health conditions. For example, it plays an important role in the modulation of the expression of the genes involved in the innate and adaptive immune system responses. In the context of vitamin D deficiency in the immune system, there appears to be an increased susceptibility to infection, and it is also prevalent in autoimmune disease.
The active form of vitamin D is a member of the endocrine system, and in this role as a hormone, it interacts with virtually every organ in the body. After absorption from dietary sources in the intestine, vitamin D is taken up in the blood stream and binds to vitamin D binding protein, which binds with vitamin D receptors in the target genes and modifies the transcription of those genes to elicit cellular responses. Vitamin D receptors are located at the liver, kidney, brain, breast, colon, cardiac muscle, thyroid, T-lymphocyte and the pituitary.
The brain is one of the most sensitive organs to insufficient levels of vitamin D. Prolonged vitamin D deficiency leads to the reduced expression of a number of genes that are involved in neurotropism, neurotransmission, neuroplasticity, and neuroprotection. It is associated with the predisposition to several neurological disorders, such as autism, multiple sclerosis, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. It is also linked to neuropsychiatric diseases such as schizophrenia and depression.
Vitamin D has been implicated in the regulation of genes that are associated with cardiovascular health, the lowering of insulin resistance, normal neuromuscular function, and the working of the thyroid gland.
Vitamin D is suspected to be a potential modulator in neurogenesis, which refers to the making of new cells and new connections in the brain. Vitamin D deficiency may play a role in a decrease in neurogenesis that may precede the decline in cognitive performance in the elderly.
Hundreds of genes with vitamin D receptor elements can directly or indirectly influence the cells in the body, such as cell cycling (the process a cell goes through each time it divides), proliferation (an increase in the number of cells because of cell growth and cell division), differentiation (the ability of the cell to become a bone cell or a heart cell or a liver cell, etc), and apoptosis (programmed cell death in which a series of molecular steps in a cell lead to its death and is a method the body uses to get rid of unneeded or abnormal cells).
Who is at risk for vitamin D deficiency?
Various factors can inhibit the production of vitamin D in the skin, such as air pollution, clothing, latitude, season, time of day, age, insulin resistance, and diet.
In terms of groups of people at risk of vitamin D deficiency, the risks already start with the unborn child and continue up to the elderly stage in life.
- Pregnancy: The vitamin D content of human milk relates to the mother’s vitamin D status. It is important for pregnant women to have their vitamin D levels checked and to take supplements as needed. Adequate levels of vitamin D may improve fetal growth and reduce the infant’s risk of conditions such as preterm-birth, gestational diabetes (diabetes diagnosed during pregnancy), small-for-gestational-age, and preeclampsia (a potentially dangerous pregnancy complication characterized by high blood pressure and protein in the urine. Sufficient levels of vitamin D during pregnancy are linked to offspring with less enamel defects, less autism, less risk for lower bone mineral content, and less attention deficit and hyperactive disorders.
- Breastfeeding: Prolonged breastfeeding with inadequate levels of vitamin D can cause rickets (weakening and softening of the bones) in infants and children. Rickets are caused by imperfect calcification and characterized by softening and distortion of the bones, typically resulting in bowlegs, delayed growth, and weakness and pain in the spine, pelvis, and legs.
- Adolescents and adults: Vitamin D deficiency can lead to a condition called osteomalacia (also referred to as “soft bones”), which is a disease that weakens bones and can cause them to break easily. It is a metabolic bone disorder characterized by the inadequate mineralization of bone tissue, which means bone breaks down faster than it can re-form. Symptoms include bones fracturing easily, pain in the bones and hips, muscle weakness, and it may include having difficulty walking.
- Older adults: As the skin’s ability to synthesize vitamin D, as well as vitamin D stores, decline with age, older adults have an increased risk of developing vitamin D deficiency. Older people may also have inadequate intake of vitamin D and are likely to spend less time outdoors with insufficient sun exposure.
- Dark skin: People with darker skin have greater amounts of the pigment melanin in the outermost layer (epidermis) of the skin, which reduces the skin’s ability to produce vitamin D from sunlight.
- Obesity: While obesity does not affect the skin’s capacity to synthesize vitamin D, it causes the absorption of greater amounts of vitamin D in the subcutaneous fat, which is a type of fat that forms the deepest layer of the skin. Obese people would need greater intakes of vitamin D.
The importance of testing for vitamin D levels.
Daily intakes of vitamin D should be sufficient to maintain bone health and normal calcium metabolism in healthy people. It is one of the essential health markers to be tested on a regular basis to not only to determine current levels, but also to monitor changes in vitamin D levels, while taking supplements.
It is important to remember that the appropriate measure of vitamin D is not the quantity of daily intake, but the achieved vitamin D blood levels. The recommended test for vitamin D status is the serum total 25-OH vitamin D levels. According to the Vitamin D Council (USA) (a scientist-led group that promotes vitamin D deficiency awareness) the ideal vitamin D levels should be between 40 ng/ml and 70 ng/ml.
Because vitamin D is fat-soluble, supplements should be taken after a full meal, as fat in the food assists with the absorption of vitamin D.
Conclusion:
The danger of Vitamin D deficiency is that people with moderate to mild deficiency are asymptomatic and have normal serum calcium and phosphorus levels. This highlights the importance of regular testing for vitamin D levels, as prolonged severe vitamin D deficiency has been associated with health outcomes such as bone disease, diabetes, hypertension, heart disease, cancer, and autoimmune and infectious diseases.
One’s vitamin D status is too important not to be aware of one’s blood vitamin D level. It should be measured annually, supplemented as required, and if of concern, more regularly monitored to ensure optimal levels.
References:
Why test vitamin D? Published 26 February 2024. Precision Point Diagnostics. (An advanced health testing laboratory.) USA. (www.precisionpointdiagnostics.com)
Vitamin D. Fact sheet for health professionals. Published online and updated 18 September 2023. Office of Dietary Supplements. National Institutes of Health. USA. (www.ods.od.nih.gov)
Vitamin D deficiency. Published online and reviewed 2 August 2022. Cleveland Clinic. USA. (A nonprofit multi-specialty medical center that integrates clinical and hospital care with research and education.) (www.clevelandclinic.org)
Time for more vitamin D. Published 1 September 2008. Harvard Health Publishing. Harvard Medical School. (www.health.harvard.edu)
Vitamin D overview. Published June 2017 in Ampathchat. Ampath laboratories. RSA. (www.ampath.co.za)
Vitamin D deficiency induces the excitation/inhibition brain imbalance, and the proinflammation shift. Published February 2020 in The International Journal of Biochemistry & Cell Biology. Science Direct. (www.sciencedirect.com)
Is vitamin D a master gene regulator? Published 29 August 2023. Cue Health. San Diego. USA. (www.cuehealth.com)
Influence of vitamin D on cell cycle, apoptosis, and some apoptosis related molecules in systemic lupus erythematosus. Published November 2015 in the Iran Journal of Basic Medicine Science. PubMed Central. National Centre for Biotechnology Information. US National Library for Medicine. National Institutes of Health. USA. (www.ncbi.nlm.nih.gov)
Vitamin D. Published online and last reviewed March 2023. The Nutrient Source. Harvard T.H. Chan School of Public Health. Harvard Medical School. (www.hsph.harvard.edu)
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