Why is there a shortage in the sunny region?
The synthesis of vitamin D in the skin is a process with many conditions, and it is enough to disrupt one of them for production to almost stop. The number of sunny days per year in itself is not a guarantee: what matters is how much ultraviolet radiation of a certain range actually reaches the exposed skin.
- Closed clothing: if only the face and hands are open, the area for synthesis is reduced significantly
- Darker skin type: melanin works as a natural filter, and for the same production you need several times more time in the sun
- Window glass and car windshield completely block the required ultraviolet range
- Working and studying indoors: Fusion peaks in the middle of the day when most people are inside
- Autumn and winter: the sun is low, and the rays pass through too thick a layer of the atmosphere to trigger synthesis
- Urban smog and high dust levels in the air further weaken ultraviolet radiation.
- Excess weight: Vitamin D is fat soluble and distributed in adipose tissue, resulting in lower concentrations in the blood
- Age: over the years, the skin's ability to synthesize significantly decreases
- Intestinal diseases, celiac disease, conditions after operations on the stomach and intestines - absorption is impaired
The shadow, by the way, is also deceptive. Under a canopy, tree or umbrella, a person receives only a small part of ultraviolet radiation, and the feeling “I've been outside all day” says nothing about synthesis. The rule is simple and rough: if your own shadow is longer than your height, the sun is too low, and practically no vitamin D is formed at this moment.
What is vitamin D responsible for and what happens when there is a deficiency?
The main and indisputable role of vitamin D is to ensure the absorption of calcium and phosphorus in the intestines and maintain normal bone mineralization. When there is not enough calcium, calcium from food is poorly absorbed, the body compensates for this by leaching calcium from the bones, and the parathyroid gland comes into play. That is why long-term deficiency is not manifested by “weak immunity”, but by a very specific bone and muscle picture.
- Aching pain in the bones - most often in the pelvis, ribs, lumbar region and legs
- Muscle weakness, especially in the hips: difficulty getting up from a chair or walking up stairs
- Increased incidence of falls in older people and fractures due to minor trauma
- In children - rickets: curvature of the legs, deformation of the chest, growth retardation and late closure of the fontanelle
- In adults - osteomalacia, softening of bone tissue with pain and a waddling gait
- Accelerated loss of bone mineral density and contribution to osteoporosis
- Nonspecific fatigue and low mood, which are often attributed to something else
We need to speak honestly about the other declared effects. Observations have indeed linked low levels of vitamin D to a variety of diseases, from infections and depression to cancer. But in studies where vitamin D was given to people with normal levels, the expected miracles did not happen. The most plausible explanation: low levels are often not a cause, but a consequence - a marker of inactivity, chronic illness, excess weight and life without the street.
Who needs analysis and who doesn't?
Mass determination of vitamin D in everyone is not recommended - this is the case when unnecessary analysis leads to unnecessary treatment. A reasonable approach is different: the analysis is carried out for those who have a high probability of deficiency or for whom the result will change tactics. For the rest, if there are risk factors, a prophylactic dose is usually sufficient without prior analysis.
- Показан: при болях в костях, мышечной слабости в бёдрах, остеопорозе, переломах при малой травме.
- Показан: при болезнях, нарушающих всасывание, — целиакия, воспалительные заболевания кишечника, состояния после операций на желудке и кишечнике.
- Показан: при хронической diseases почек, заболеваниях печени, приёме противосудорожных препаратов и глюкокортикоидов.
- Показан: при выявленном нарушении кальциевого обмена, повышенном паратгормоне, мочекаменной болезни.
- Показан: у детей с признаками рахита и у пожилых людей с повторными падениями.
- Обычно не нужен: здоровому взрослому без жалоб и факторов риска — при наличии факторов риска можно сразу принимать профилактическую дозу и не тратиться на анализ.
- Не нужен: для контроля каждые один-два месяца на фоне обычной профилактической дозы — показатель меняется медленно.
If the test still passes, the right choice is important: 25-hydroxyvitamin D is determined, which reflects the reserve in the body. Another indicator, the active form of the vitamin, is prescribed in rare situations at the discretion of the doctor, and is not suitable for assessing the supply - if there is a deficiency, it can remain normal and create false reassurance.
How to read the result
Laboratories use two units of measurement, and this regularly leads to confusion: the same value looks like 30 in some units and 75 in others. Before you get scared by the numbers, it’s worth looking at how they are expressed.
- Deficiency - below 20 ng/ml, that is below 50 nmol/l
- Deficiency - approximately 20–30 ng/ml, or 50–75 nmol/l
- Sufficient level - above 30 ng/ml, or above 75 nmol/l
- The benchmark that one usually strives for is a corridor of approximately 30–60 ng/ml
- The alert zone is above 100 ng/ml: long-term retention of such values is undesirable
- The conversion is approximate: the value in ng/ml is multiplied by approximately 2.5 to obtain nmol/l
Another detail that is rarely thought about. Vitamin D levels fluctuate naturally throughout the year: they are higher in late summer and lower in late winter. An analysis taken in February and an analysis taken in August for the same person can differ significantly, and it is correct to compare dynamics only when adjusted for the season.
How to replenish: sun, food and supplements
The three sources solve the problem very differently, and understanding their real contributions eliminates wasted effort. The sun is the most natural path, but poorly controlled; food is the most attractive, but practically powerless; additives are the most predictable.
- Sun: Brief exposure to open sun in the middle of the day with arms and legs exposed—usually a short amount of time for fair skin and noticeably longer for dark skin. There is no need to intensify the tan: synthesis does not increase redness, and the harm from it is real
- Fatty sea fish - salmon, mackerel, herring, sardines - are the only truly rich food source
- Cod liver is a very concentrated source, but it is easy to overload with vitamin A, so it is not eaten regularly and in large quantities.
- Egg yolk, butter, liver - make a small contribution
- Mushrooms grown under ultraviolet light contain a different form of the vitamin that works less well
- Fortified foods, if available, provide a stable, small supplement
- Colecalciferol preparations are the main way to actually close the deficiency; the dose is selected by the doctor based on the initial level, weight and concomitant diseases
A simple calculation shows why you can’t rely on food in this matter: to get the daily requirement from food, you would have to eat fatty fish almost every day, and you would need an incredibly large amount of yolks. In a real diet, where fish appear once a week, the contribution of food remains modest. This is not an argument against fish - it has many other advantages - but an argument against the hope of closing the gap with nutrition alone.
Overdose: why “the more the merrier” doesn’t work
Unlike water-soluble vitamins, the excess of which is simply excreted, vitamin D accumulates in adipose tissue and the liver. That is why long-term use of excessive doses can lead to overload. The mechanism is clear: excess vitamin D increases calcium absorption, calcium in the blood increases, and the kidneys, blood vessels and nervous system suffer.
- Early manifestations of excess calcium: weakness, nausea, loss of appetite, constipation, extreme thirst and excessive urination
- Further - headache, confusion, heart rhythm disturbances, bone pain
- Calcium deposition in the kidneys and stone formation, decreased kidney function
- The risk is greater in people taking large doses of calcium at the same time.
- Particular caution is needed for sarcoidosis, tuberculosis and some other diseases in which sensitivity to vitamin D is increased
- Separate risk in infants when parents independently increase the dose
“Shock doses” deserve a separate discussion - single doses of a very large amount of the vitamin, which are sometimes prescribed for quick replenishment. The convenience is obvious, but in older people, this tactic was surprisingly associated not with a decrease, but with an increase in the number of falls. Therefore, daily or weekly use of a moderate dose is preferable, and single large doses are used for specific indications and not for convenience.
