In recent years, the importance of vitamin D in our health has been increasingly emphasized and many articles have been published on this subject. Apart from the effects of vitamin D on bone health, its preventive effect on cancer, autoimmune conditions, cardiovascular diseases and some chronic diseases is mentioned. Since most of vitamin D is synthesized in the skin by ultraviolet exposure, dermatologists should know this issue very well. In this article, I will talk about the beneficial and harmful effects of vitamin D on both our skin and our health.
Vitamin D Sources
Vitamin D is a fat-soluble hormone and its main function is to maintain calcium-phosphorus balance and is to protect bone health. It is popularly called the sun vitamin due to its antirachitic properties. It exists in two main forms, D2 and D3. Ultraviolet radiation is responsible for more than 90% of vitamin D synthesis. Vitamin D3 form (cholecalciferol) is synthesized from 7-dehydrocholesterol (7-DHK) by keratinocytes and fibroblasts in the basal and suprabasal layers of the epidermis under the influence of UVB at a wavelength of 290-320 nm (maximum effect 300±5nm). Vitamin D can also be obtained with food. Vitamin D3 is found especially in fatty fish (such as salmon, tuna, mackerel, sardine), and to a lesser extent in egg yolk and beef liver. One serving of sea salmon contains 800-1000 IU of vitamin D, which is reduced by 1/4 in farmed salmon. One egg yolk contains 40 IU of vitamin D. Vitamin D2 (ergocalciferol) is of plant origin and is found in some mushroom species. In some countries, such as the USA, some of the daily consumed nutrients (milk, yoghurt, butter, margarine, orange juice, breakfast cereals) are enriched with vitamin D. These two forms of vitamin D, which are considered functionally equivalent, are first converted to 25-hydroxy vitamin D (calcidiol) in the liver and then to 1,25 dihydroxy vitamin D (calcitriol) in the kidneys. Since the half-life of 25(OH) vit D is a few weeks, it is an indicator of the body's vitamin D storage. Normal values are between 20-100 ng/ml (50-250nmol/L). In terms of general health, it is recommended that the optimal level be 30 ng/ml (75nmol/L) and above. Serum 1,25(OH)2 vit D levels do not indicate the vitamin D reserve in the body. That's why there's no point in looking at it.
D Vi Vitamin D Deficiency and Toxicity
Serum 25(OH) vit D level below 20 ng/ml (50nmol/L) is considered as vitamin D deficiency. While values between 12-20 ng/ml (30-50 nmol/L) have negative effects on skeletal health and general health, serious deficiency states below 12 ng/ml (30 nmol/L) are indicative of vitamin D deficiency and lead to rickets in children and osteomalacia in adults. opens. Excessive vitamin D intake can lead to toxicity. It is not possible to synthesize excessive amounts of vitamin D with sunlight. With ultraviolet light less than a minimal erythema dose (MED), that is, the dose that causes redness on our skin, vitamin D synthesis increases to maximum levels and more UV-inactive forms are formed, thus the balance of vitamin D synthesis in the skin is achieved. Vitamin D toxicity does not develop with diet, except for excessive amounts of fish oil intake. However, taking high daily doses of vitamin D pills for a long time can lead to toxicity. Intake of up to 4000 IU per day is considered safe. It has also been shown that short-term use of high doses (e.g. 50,000 IU weekly for 8 weeks) does not cause toxicity. However, a single dose of 300,000 IU vitamin D has serious side effects on heart health. Serum 25(OH) vit D level above 200 ng/ml (500 nmol/L) is potentially toxic. Symptoms of vitamin D toxicity are nausea, vomiting, loss of appetite, constipation, fatigue and weight loss. High levels of calcium can lead to mental changes, confusion, and cardiac arrhythmias. According to the results of cohort studies conducted by the American National Cancer Institute in more than two million cases, chronic 25(OH) vit D levels above 40 ng/ml (100nmol/L) increase the risk of pancreatic cancer. Although the risk rate of vitamin D supplementation alone in kidney stone formation is not fully known, it has been shown that the combined use of 1000 mg calcium daily and 400 IU vitamin D supplementation for 7 years in postmenopausal women increases kidney stone formation by 17%.
D Factors Effective in Vitamin Synthesis
Age, skin color, absorption from the gastrointestinal tract, latitude and altitude of the place of residence, season, hours of sun exposure, weather conditions such as fog and clouds, shape of clothes, The use of sunscreen cream, obesity and the use of some medications affect the synthesis of vitamin D.
It has been shown that the elderly synthesize 1/4-1/5 of vitamin D compared to people under the age of 30.
It is necessary to synthesize the same amount of vitamin D. People with fair skin need to sunbathe for longer periods of time than those with fair skin. Most of the vitamin D is absorbed from the small intestine. Therefore, people with intestinal absorption problems are at risk of vitamin D deficiency. It is recommended that vitamin D levels be monitored under the control of an endocrinologist in people with inflammatory bowel disease, Whipple's disease, cystic fibrosis, and celiac disease. Some drugs, especially epilepsy drugs, cortisone, rifampin, HIV/AIDS drugs and St. The use of St. John's wort reduces the level of vitamin D. The latitude of the place of residence also affects vitamin D synthesis. In countries above 35 degrees latitude, it is considered that there are no UVB rays during the winter months, and vitamin D synthesis is not possible. Our country is between 36-42 northern latitudes. For this reason, vitamin D synthesis differs in people living in the north and south of Turkey.
Winter months, exposure to the sun outside the noon hours, air pollution, cloudy weather, the thickness of the ozone layer, low altitude reduce the synthesis of vitamin D. Lifestyle and dressing habits also affect vitamin D synthesis.
If the body mass index is over 30, that is, in obese people, vitamin D deficiency occurs because vitamin D accumulates in fat tissue.
The whole body is in a MED state. 10,000-20,000 IU of vitamin D is synthesized by exposure to the sun. 3,000 IU vitamin D is synthesized as a result of exposure of the arms and legs to a half dose of MED. Exposure of the face, arms and legs to midday sun for 5-30 minutes twice a week is sufficient for the synthesis of vitamin D in Caucasians. Less than one MED is sufficient for vitamin D synthesis in the skin, and as a result of more UVB, inactive metabolites are synthesized and balance is achieved. Vitamin D is synthesized when more than 19% of the body is exposed to sunlight. If appropriate amounts of sunscreen creams are applied to the whole body, vitamin D synthesis is prevented. However, sunscreens do not block all UVB. Even if a GPF 30 preservative is applied in sufficient quantity, 1/30, i.e. 3.3% erythemal dose is taken. Moreover, although the amount required to be applied is 2mg/cm2, it has been shown that people generally use 0.5 mg/cm2. Not applying it to all open areas, skipping some areas such as the ears, neck and feet, and not re-applying it sufficiently does not completely prevent UVB and therefore vitamin D synthesis. In addition, many people use sunscreen creams to sunbathe for longer periods of time without sunburn.
Recommended Daily Vitamin D Doses
Those with vitamin D deficiency must be treated; the necessary daily vitamin D must be taken with food and It is recommended to take it as a vitamin supplement if necessary. However, vitamin D synthesis through sunbathing should not be recommended. The American Institute of Health announced its latest recommendations regarding vitamin D in November 2010. These recommendations are based on proven data on vitamin D's skeletal health. No recommendation has been made because the effect of vitamin D on conditions such as cancer, cardiovascular diseases, diabetes mellitus and autoimmune diseases has inconclusive or contradictory results. Since the synthesis of vitamin D by sun exposure is affected by many factors (such as season, day time, weather conditions, skin pigmentation) and increases the development of skin cancer, daily recommended doses are made for conditions where sun exposure is absent or minimal. Recommended doses of vitamin D; It is 400 IU/day for ages 0-1, 600 IU/day for ages 1-70, and 800 IU/day for people over 70 years of age. 600 IU/day vitamin D is recommended for pregnant and breastfeeding women. According to another calculation; Daily intake of 100 IU vit D increases serum 25(OH) vit D by 1.0 ng/ml (2.5 nmol/L). According to this calculation, it is necessary to take 1000 IU of vitamin D daily to prevent deficiency (< 10 ng/ml) in conditions where there is no vitamin D synthesis through diet or UV.
When to Check Serum Vitamin D Levels?
It is recommended to check vitamin D levels in people at risk for vitamin D deficiency. Because checking serum 25(OH) vitamin D levels in everyone will put a burden on the health economy. People at risk; elders, religious or cultural Those who do not go out in the sun for various reasons or dress modestly, those who are protected from the sun very closely (such as xeroderma pigmentosum, SLE, basal cell nevus syndrome, photosensitivity, kidney, bone marrow and liver transplantation patients), those with malabsorption and those who are obese. Breastfed babies are at risk of vitamin D deficiency. Because breast milk contains only 25 IU/L of vitamin D.
Vitamin D and Skin Cancer
The UVB spectrum that plays a role in vitamin D synthesis is also the wavelength responsible for sunburns and photocarcinogenesis. It has been recommended to avoid the sun for more than forty years. Despite this, the incidence of skin cancer and the health budget allocated to it are increasing. Having six sunburns in a lifetime increases the risk of both melanoma and non-melanoma skin cancer. UV radiation is also involved in skin aging and immunosuppression. However, it is difficult to change social habits such as tanning, wearing less clothing, and vacationing in sunny countries. Due to the increasing incidence of melanoma and non-melanoma skin cancers, raising awareness about the harmful effects of the sun and the correct use of sunscreen products is very important. Especially dermatology physicians need to embrace this issue. At this stage, discussions about inhibiting vitamin D synthesis come to the fore. Studies have yielded different results. Marks et al. They reported that there was no difference in vitamin D synthesis between those who used sunscreen and those who did not. Farrerous et al. They stated that vitamin D synthesis decreased by 31-35% in those who used sunscreen during the winter months and by 17-40% in those who did not use it, and increased by 35%-33% in the first and second years, respectively, in those who used sunscreen in the summer months and by 55%-24% in those who did not use it. In another study, vitamin D levels were found to be correlated with the use of sunscreen cream, and this result was interpreted as people using sunscreen cream to stay in the sun for longer periods of time without sunburn.
Effects of Vitamin D on General Health
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