Vitamin D3 deficiency in winter: An underestimated health risk
As the days get shorter and the amount of sunlight decreases in winter, the risk of vitamin D3 deficiency increases significantly. Vitamin D3, also known as the "sun vitamin", plays a crucial role in our health. It not only supports bone maintenance and the immune system, but also influences mood and general well-being. But why is winter a critical time for our vitamin D3 levels and what can we do about it?
Why winter is a problem
Vitamin D3 is mainly produced in the skin through exposure to UVB rays from the sun. In the winter months, however, sunlight in many parts of the world is not strong enough to ensure sufficient production. Particularly in northern Europe or in regions with frequent cloud cover, people also spend more time indoors, which further reduces natural vitamin D production.
The consequences of a defect
A persistent deficiency of vitamin D3 can have significant health consequences, as this vitamin plays a key role in numerous biological processes at a molecular and physiological level. The scientific and medical perspective is explained in detail below:
1. vitamin D3 - basics and function
Vitamin D3 (cholecalciferol) is a fat-soluble prohormone that is synthesised in the skin from 7-dehydrocholesterol under UV-B radiation. It is hydroxylated in the liver to 25-hydroxyvitamin D (calcidiol) and in the kidneys to 1,25-dihydroxyvitamin D (calcitriol). The latter is the biologically active form of vitamin D3.
Calcitriol acts as a hormone and binds to the vitamin D receptor (VDR), a nuclear receptor that controls gene expression. Over 200 genes that are involved in important biological processes are regulated by vitamin D. These include genes associated with cell proliferation, the immune response and calcium metabolism.
2. the effects of vitamin D3 deficiency at the molecular level
A vitamin D3 deficiency has a profound effect on numerous molecular processes:
- Calcium and phosphate homeostasis: Vitamin D regulates the expression of proteins such as TRPV6 (calcium channels) and calbindin, which are crucial for intestinal calcium absorption. Without sufficient vitamin D, the serum calcium level drops, which stimulates the release of calcium from the bones (parathyroid hyperactivity).
- Gene regulation: The vitamin D receptor is expressed in almost all cell types. A deficiency influences the regulation of genes that are involved in inflammatory processes, cell division and differentiation.
3 Clinical effects of vitamin D3 deficiency
3.1 Bone health
- Mechanism: Vitamin D3 increases the intestinal absorption of calcium and phosphate. A deficiency leads to secondary hyperparathyroidism, whereby bones are broken down to release calcium.
- Consequences of a deficiency: Insufficient mineralisation of the bone matrix in adults, which leads to bone pain and deformation (osteomalacia). Chronic deficiency increases the risk of porous bones and bone fractures, especially in old age(osteoporosis). Malformations and growth disorders in children, such as bent bones(rickets).
3.2 Immune system
- Mechanism: Calcitriol modulates the activity of immune cells, including T cells and macrophages. It suppresses pro-inflammatory cytokines (e.g. TNF-α, IL-6) and promotes anti-inflammatory mediators.
- Consequences of a deficiency: Increased susceptibility to infections (e.g. respiratory infections) and chronic inflammatory conditions, which can contribute to autoimmune diseases such as multiple sclerosis, type 1 diabetes and rheumatoid arthritis.
3.3 Muscle function
- Mechanism: Vitamin D regulates calcium channels and muscle cell contraction.
- Consequences of a deficiency: muscle weakness and pain and therefore an increased risk of falling, especially in older people.
3.4 Mental health
- Mechanism: Vitamin D influences the synthesis of serotonin and dopamine as well as neurotrophic factors such as nerve growth factor (NGF).
- Consequences of a deficiency: Higher risk of depression and cognitive impairment. Increased likelihood of seasonal affective disorder (SAD).
3.5 Cardiovascular system
- Mechanism: Vitamin D influences endothelial function and the renin-angiotensin-aldosterone mechanism.
- Consequences of a deficiency: Increased risk of high blood pressure, heart failure and cardiovascular events (e.g. myocardial infarction).
3.6 Cancer
- Mechanism: Vitamin D inhibits cell proliferation and promotes cell differentiation through gene regulation.
- Correlations: Low vitamin D levels are associated with a higher risk of breast, bowel and prostate cancer.
4. scientific evidence
A meta-analysis from 2019 highlights the critical role of vitamin D3 for health: it showed that low vitamin D levels of less than 30 nmol/l are associated with a significantly increased risk of increased mortality from all causes. These results emphasise the far-reaching systemic effects of a deficiency. Higher rates of autoimmune diseases and seasonal depression were found, particularly in northern countries where UV-B exposure is greatly reduced during the winter months. These correlations illustrate how essential an adequate supply of vitamin D is not only for physical health, but also for mental health.
5. causes of a defect
Vitamin D deficiency can be favoured by a variety of factors that are closely linked to geographical, genetic, lifestyle and health aspects. People living in higher latitudes such as Europe are particularly at risk in winter, as UV-B radiation is not sufficient to produce enough vitamin D in the skin during this time. Skin colour also influences the body's own synthesis: people with darker skin have a higher melanin content, which reduces UV-B-dependent vitamin D production.
Modern lifestyle also plays a decisive role. Little sun exposure due to predominantly office work, spending time indoors and the frequent use of sunscreen considerably limits vitamin D production. Dietary patterns often further increase this risk, as vitamin D-rich foods such as fatty fish, egg yolk or fortified products are rarely included in many diets.
Finally, certain illnesses can also impair the vitamin D supply. Chronic kidney or liver disease disrupts the activation of vitamin D, as the organs required to convert it into its active form do not function properly. This combination of internal and external factors makes an adequate supply of vitamin D particularly challenging for many people.
6. prevention and treatment of vitamin D deficiency
Diet: A balanced diet containing foods rich in vitamin D supports the supply. Oily fish such as salmon, mackerel and herring, which are natural sources of vitamin D, are particularly recommended. Cod liver oil, egg yolk and fortified products such as milk, orange juice or breakfast cereals also help to cover the requirement. However, diet alone is often not enough to achieve sufficient vitamin D levels, especially in regions with low levels of sunlight.
Supplementation: In cases of vitamin D deficiency or increased need, for example during the winter months, it is often recommended to take dietary supplements. A daily dose of 800-2,000 IU (International Units) is considered safe and effective to compensate for deficiencies. In the case of severe deficiency or certain risk groups, such as people with chronic illnesses or older people, a higher dosage may be necessary after consultation with a doctor.
Diagnosis: Vitamin D deficiency is diagnosed by measuring the 25-hydroxyvitamin D level in the serum, which is considered a reliable marker for vitamin D supply. Values in the range of 50-100 nmol/l are optimal. Values below 30 nmol/l indicate a significant deficiency and require therapeutic measures. Regular medical check-ups are particularly useful for people at risk or during treatment in order to adjust the dosage and avoid a possible excess (hypervitaminosis D).
A holistic approach that combines sun exposure, nutrition and, if necessary, supplementation is crucial to ensure the vitamin D supply and minimise the associated health risks.