Winter presents many challenges to our health. As I've mentioned several times in my earlier articles, damp and cold weather particularly promote viral colds. In winter, the days become shorter, and we face a period with little light and sunshine. While daylight can last up to 17 hours in summer, the shortest day in winter has only 8 hours.
Why is this important in this context? Because vitamin D is primarily produced in the skin through UV-B radiation from sunlight. UV-B radiation converts a cholesterol precursor into vitamin D3. This is then converted in the liver into a storage form and in the kidneys into the active hormone form, calcitriol.
But it's not just sunlight, but above all the intensity of solar energy that is important for vitamin D production, and this also varies seasonally. Due to the steeper angle of incidence of the sun in summer, the energy yield is up to 10 times higher than in winter .
Similarly, we can only produce relevant amounts of vitamin D if we expose a sufficient area of skin to the sun. Even with good sun exposure, we need to expose at least 20% of our skin surface (approximately both arms and legs) to produce enough vitamin D. Skin type and time of day are further factors that influence vitamin D production.
However, as I frequently observe in my daily practice through simple blood tests, many people's vitamin D stores are insufficiently replenished. Yet vitamin D is a crucial vitamin that fulfills many important functions in the body.
Vitamin D is primarily known for its role in bone health and osteoporosis prevention , as it regulates calcium and phosphate metabolism.
Vitamin D is also crucial for muscle function , as it supports muscle development, strength, performance and regeneration by promoting protein synthesis and reducing inflammation; a deficiency often leads to muscle weakness and an increased risk of falls, especially in older age.
Vitamin D plays an important role in modulating the immune system . It influences the immune response by regulating the balance between pro-inflammatory and anti-inflammatory substances, thereby potentially reducing susceptibility to infection. During the COVID-19 pandemic, there was an increased mortality rate among patients with vitamin D deficiency.
Less well-known is the influence of vitamin D on mental health . Vitamin D is involved in the production of the neurotransmitter serotonin, which is crucial for mood. It also affects dopamine and norepinephrine. A vitamin D deficiency is associated with an increased risk of mental health conditions such as depression and anxiety. In winter, psychiatric clinics and hospitals see an increase in symptoms such as fatigue and lack of motivation. Therefore, vitamin D is also known as the "happy vitamin."
If we don't produce enough vitamin D through our skin, it must be obtained from external sources . Only small amounts are absorbed through food (e.g., eggs, fatty fish, mushrooms). Therefore, we usually need to take vitamin D as a supplement. Bioavailability depends on individual factors such as age and fat digestion, with D3 from algae often being better absorbed, and taking it with fat increasing the absorption of supplements. However, the effectiveness of vitamin D also depends on the function of the vitamin D receptor (VDR), which can vary considerably from person to person. Modern genetic analyses can now determine VDR function.
The combination of vitamin D and vitamin K2 is recommended, as both vitamins have a synergistic effect on bone metabolism. Vitamin K2 plays a crucial role by transporting ingested calcium to where it belongs – the bones. It activates specific proteins, such as osteocalcin, which incorporate the calcium into the bone structure, thus maintaining bone density and strength.
Taking these two vitamins together is also important for the cardiovascular system. While vitamin D3 increases calcium absorption, it's crucial to ensure that this calcium isn't deposited in the arteries or other soft tissues. Vitamin K2 activates another protein called MGP (matrix Gla protein), which inhibits calcium deposits in blood vessels, thus helping to reduce the risk of cardiovascular disease.
The recommended vitamin D dosage varies depending on age and individual circumstances . The maintenance dose is generally 2,000–4,000 IU per day , or approximately 20,000 IU per week . The dose can be increased in cases of deficiency. Recent findings indicate that fractionated daily dosing leads to better, more consistent absorption and utilization of vitamin D.
When taking vitamin D, it's important to remember that, as with all fat-soluble vitamins (E, D, K, A; think of it like the "EDEKA" vitamins in German), overdoses can occur due to storage in fatty tissue, potentially leading to side effects. Therefore, regular blood tests (approximately once a year) are recommended.
PDB Supplements offers aprecisely dosed liquid vitamin D3/K2 combination . Our vitamin D is dissolved in high-quality MCT oil from coconut to guarantee maximum bioavailability. With 1000 IU per drop, it can be easily and precisely dosed. The liquid form allows it to be taken with fatty meals. Sprinkled over muesli with yogurt or on a cheese sandwich in the morning, it can be absorbed quickly and efficiently.