By Andri Vassiliou, dietitian:
Vitamin D is a fat-soluble vitamin that is formed in the body mainly through the absorption of solar ultraviolet radiation by the skin, but also by certain foods rich in vitamin D.
The two forms (metabolites) of vitamin D are ergocalciferol (vitamin D2) which is included in food and cholecalciferol (vitamin D3) which is produced in the skin through its exposure to the sun's ultraviolet rays.
It is necessary for the absorption and utilization of calcium and phosphorus by the intestine. In conjunction with other hormones (eg calcitonin) it regulates the concentration of calcium in the blood according to the needs of the body, as well as its deposition or removal from the bones, thus promoting the formation of bones and teeth. It is involved in neuromuscular function and a number of other cellular functions, such as the proper functioning of the immune system.
Main source of vitamin D.
Most of the daily needs for vitamin D are covered by the body's ability to synthesize it when the skin is exposed to the sun.
The amount of vitamin D produced in the body depends on:
1) the time of the exhibition,
2) the area of exposed skin,
3) the wavelength of the radiation,
4) the degree of air pollution,
5) skin color (high concentration of melanin requires more exposure to achieve the same degree of composition) and
6) the age of the individual (the elderly have half the ability to make up compared to the young).
Thus, more vitamin D is produced during the noon than in the early morning or late afternoon. Also, in the shade or during a cloudy day a smaller amount is produced. It is worth mentioning, however, that excessive sun exposure can lead to immediate (skin burns, photokeratitis in the eyes) and chronic (cataracts, keratopathy, premature skin aging, skin cancer) health problems. Thus, it is good to be exposed to the sun for 10-15 minutes 3 times a week, avoiding exposure between 11 a.m. and 4 p.m., especially during the summer months, when UV radiation is dangerous.
What is the importance of diet for vitamin D intake
When sun exposure is insufficient (eg prolonged cloudiness, reduced sunshine, heavy clothing, avoidance of sun exposure), the importance of nutrition in meeting daily needs is much greater.
Main sources of vitamin D are the liver, fish oils, egg yolk, some fish (herring, salmon, tuna, sea bass, sea buckthorn, sardines), fortified margarines, fortified dairy products. Because vitamin D is a fat-soluble vitamin, it requires the simultaneous intake of a source of fat to be absorbed by the body. So, if you want to increase the intake of vitamin D through food, it would be good to avoid fortified 0% dairy or at least combine them with some fat source.
The daily needs for vitamin D.
• Infants and adults up to 50 years old: 200IU (international units)
• Adults from 51 to 70 years: 400 IU
• People over 70 years: 600 IU
Who is at risk for Vitamin D deficiency
• People with limited exposure to sunlight.
• Excessive use of sunscreen.
• People with dark skin.
• The urbanization and the trend of working indoors, as well as some clothing habits of some peoples.
• Breastfed infants and developing children.
• Pregnant women and those who are breastfeeding.
• Postmenopausal women, who have an increased risk of osteoporosis.
• People over the age of 50, because the ability to synthesize vitamin D decreases with age.
• People with fat malabsorption conditions such as celiac disease, Crohn's disease, cystic fibrosis and pancreatitis.
• People with liver and kidney disease or enzyme deficiencies.
• People living in the northern hemisphere (latitude greater than 35 °) especially during the winter.
• Hypoparathyroidism
•Obese people.
What are the risks of Vitamin D deficiency?
• In children it can cause Rickets, a bone disease that leads to poor growth with weak bones, delayed growth and immunodeficiency.
• In adults it can also affect good bone health causing Osteomalacia and Osteoporosis. About 6% of men and more than 20% of women over the age of 50 suffer from osteoporosis, while 1 in 5 men and 1 in 3 women will suffer an osteoporotic fracture after the age of 50. Also, 75% of women who have osteoporosis do not know it.
Vitamin D deficiency can lead to newborns and young children for the rest of their lives at risk of developing Rheumatoid Arthritis, Diabetes, Parkinson's, Alzheimer's, Multiple Sclerosis, inflammatory bowel infections, all due to poor immune system function.
People with low vitamin D levels may develop cancer of the rectum and intestine, endometrium, breast, skin, pancreas, prostate or lymphoma.
• Low levels of vitamin D have been linked to risk factors for cardiovascular disease such as hypertension, myocardial infarction, congestion, heart failure and diabetes.
What happens when there is hypervitaminosis
Vitamin D in large quantities can be toxic, as as a fat-soluble vitamin it is stored in body fat. Vitamin D toxicity is not common, but it is not impossible to occur. Hypervitaminosis is possible due to excessive consumption of foods fortified with vitamin D or by overdose of vitamin D supplements. Children are more vulnerable to hypervitaminosis than adults.
Intake of large doses leads to hyperkalemia with its accompanying symptoms (apathy, anorexia, diarrhea, dry mouth, fatigue, headache, nausea and vomiting, thirst and weakness). Hypervitaminosis also leads to diarrhea, weight loss, loss of muscle tone, deafness, damage to the kidneys, heart, lungs, blood vessels and other soft tissues and even death. While normal vitamin D intake prevents osteoporosis, chronic overdose has the opposite effect leading to osteoporosis.
Andri Vassiliou - Dietitian