One nutrient that is crucial to your health and performance but is sometimes disregarded when winter approaches and daylight hours decrease is vitamin D. Understanding vitamin D is crucial, whether you're an athlete aiming for a new PB, a busy professional balancing work and training, or just someone trying to keep healthy over the winter.
This article will discuss the true functions of vitamin D in the body, the reasons why deficiency is so prevalent during the winter, the warning signals of low levels, and how to maximize your levels through diet, supplements, and wise lifestyle decisions. Now let's get started.
What is Vitamin D and Why Does It Matter?
The reason vitamin D is sometimes referred to as the "sunshine vitamin" is that sunlight causes your skin to create it. However, referring to it as a vitamin minimizes its significance. Vitamin D affects almost every system in your body and brain, acting more like a hormone (Caccamo, Ricca et al. 2018).
This is why it's so important:
Bone health: Your gut's absorption of calcium is regulated by vitamin D (Carmeliet, Dermauw et al. 2015, Fleet 2022). Your body cannot adequately absorb calcium from the diet without enough vitamin D, which weakens bones over time and raises the risk of fracture (Wang, Chen et al. 2020). Everyone is concerned about this, but we exercise enthusiasts who put a lot of strain on our bodies are most affected.
Immune Function: According to Wei and Christakos (2015), vitamin D is essential for boosting your immune system. According to research, having enough vitamin D helps your body fight off respiratory infections, which is especially important in the winter when colds and the flu are common (Prietl, Treiber et al. 2013, Carlberg 2019, Bishop, Ismailova et al. 2020).
Actually, both your innate immune response—your first line of defense—and adaptive immunity—your tailored response to particular pathogens—are supported by vitamin D. Because of this, vitamin D is essential during the winter months when respiratory infections are prevalent (Charoenngam and Holick 2020, Daryabor, Gholijani et al. 2023).
Muscle Function: You might not be aware that muscle tissue has vitamin D receptors, which have an impact on muscle strength, recuperation, and protein synthesis (Montenegro, Cruzat et al. 2019). Reduced muscle function and a higher risk of injury in athletes have been associated with low vitamin D levels (Yoon, Kwon et al. 2021, Agoncillo, Yu et al. 2023, Carswell, O'Leary et al. 2023).
Mood and Mental Health: Seasonal Affective Disorder (SAD) peaks in the winter for a reason. Low levels of vitamin D are linked to depressed mood, brain fog, and diminished cognitive performance because it affects neurotransmitter production and brain function (Spedding 2014, Farghali, Ruga et al. 2020, Pertile, Brigden et al. 2023).
Inflammation control: Vitamin D aids in controlling the body's inflammatory reactions (Infante, Buoso et al. 2021, Mieszkowski, Borkowska et al. 2021, Ziada, Wishahe et al. 2025). This is crucial because persistent low-grade inflammation hinders healing, raises the risk of injury, and jeopardizes long-term health (Fulop, Larbi et al. 2021). Consider vitamin D as the lubricant that keeps several engines operating efficiently. Little problems with your immune system, brain, muscles, and bones might worsen as levels fall.
The Winter Problem: Why We're All at Risk
The problem is that exposure to sunshine provides the majority of our vitamin D. The active form of vitamin D3 (cholecalciferol) that your body uses is created when UVB rays strike your skin.
Winter, however, throws a wrench in the plans. Even on clear days, UVB photons are insufficient to promote vitamin D production in the UK between October and March due to the sun's angle (Prentice 2016).
Include:
- Reduced hours of daylight
- Spending more time indoors
- Wearing bulky clothing outside
- Cloudy skies
You also have the ideal conditions for deficiencies.
Up to 50% of people worldwide may be vitamin D deficient, according to research, and this number rises dramatically in northern latitudes throughout the winter (Cosentino, Campodonico et al. 2021). You're much more at risk if you work long hours, train indoors, or just don't prioritize outdoor time.
Signs You Might Be Low in Vitamin D
Although there aren't often clear symptoms of vitamin D insufficiency, there are certain indicators to be aware of:
- Persistent exhaustion despite getting enough sleep
- Recurrent infections or colds
- Feeling depressed, agitated, or uninterested
- Weakness in the muscles or a delayed recovery from exercise
- Stiffness or discomfort in the joints
- Stress fractures or poor bone health (in difficult situations)
- Fogginess or trouble focusing
Checking your vitamin D levels is worthwhile if any of these symptoms sound familiar. Although most general health standards describe ≥50 nmol/L as sufficient, many sports-medicine specialists recommend serum 25(OH)D of at least 75 nmol/L for active people and athletes, with others recommending 80–100 nmol/L as a desirable range (Yoon, Kwon et al. 2021, Ip, Fu et al. 2022).
How to Optimise Vitamin D in Winter?
The good news? You're not helpless. The best ways to keep vitamin D levels in check throughout the winter are as follows:
1. Go outside whenever you can.
Outdoor exposure is important even though winter sunshine in the UK won't produce vitamin D. Natural light improves mood, promotes physical activity, and helps control your circadian rhythm. Every day, try to spend at least 20 to 30 minutes outside, preferably in the morning.
Make the most of your winter travels to regions with more sunshine. Vitamin D production on the arms and legs can be greatly increased by brief sun exposure (10–30 minutes, depending on skin tone) (Webb, Kazantzidis et al. 2018).
2. Give Vitamin D-Rich Foods Priority
Even if it's challenging to get all the vitamin D you need from your diet, every bit counts. The top food sources consist of:
- Fish high in fat (trout, salmon, mackerel, and sardines)
- Egg yolks (preferably from eggs reared on pasture)
- Certain dairy products, plant milks, and cereals are examples of fortified foods.
- UV-exposed mushrooms
- Liver oil from cod
An egg yolk has about 40 IU of vitamin D, compared to 500–600 IU in a 100g plate of salmon. Food by itself won't get you there, but it helps. For background, several experts advise consuming 1000–2000 IU per day during the winter.
Also Read: Everything You Need to Know About Diet Protein
3. Strategically Supplement
Winter supplementation is mandatory for the majority of UK residents. Here are some things to think about:
Form: Select cholecalciferol, or vitamin D3, instead of ergocalciferol, or vitamin D2. Blood levels can be raised and maintained more successfully with D3 (van den Heuvel, Lips et al. 2024).
Dosage: For maintenance, 1000–2000 IU per day is a reasonable place to start. Depending on baseline levels, body weight, and activity levels, many people require greater dosages (3000–6000 IU for specific periods of time) (Yoon, Kwon et al. 2021). To get your ideal dosage, get tested and see a medical expert if you're not sure.
Take with fat: Because vitamin D is fat-soluble, taking it with a meal that contains dietary fat improves its absorption.
Timing: Taking vitamin D in the morning may be more in line with your body's natural circadian rhythms, but there is no magic moment. Timing is not as important as consistency.
4. Keep an Eye On Your Levels
Checking your vitamin D levels twice a year—once at the end of summer, when levels are at their greatest, and once in winter, when they are at their lowest—is a good idea if you're serious about optimizing both performance and health. This gives you a clear picture of how successful your supplements strategy is.
Special Considerations for Athletes
Vitamin D becomes even more crucial if you're working out hard. According to research, raising low vitamin D levels aids in:
- Improved strength and muscular function (Wyatt, Reiter et al. 2024; Han, Xiang et al. 2024)
- Faster healing and less inflammation (Giustina, Bilezikian et al. 2024)
- Reduced rates of injuries (Yoon, Kwon et al. 2021)
- Enhanced immunity during periods of intense exercise (Jung, Seo et al. 2018)
Athletes already face difficulties during the winter, including fewer days, colder temperatures, and an increased chance of disease. Don't let low vitamin D complicate matters, please. Supplementation should be considered an integral element of your training regimen rather than an afterthought.
The Bottom Line
A fundamental nutrient, vitamin D affects bone health, immunological response, muscle function, mood, and inflammatory regulation.
For people who live in northern latitudes, winter makes insufficiency nearly certain, but the remedy is simple: spend as much time outside as possible, eat foods high in vitamin D, and take D3 supplements when needed.
Consider evaluating your levels and modifying your strategy if you're working out hard, coping with regular illness, or feeling depressed and short on energy.
High-quality, WADA-compliant vitamin D3 at 3000 IU per spray is part of Kinetica Sports' supplement line. Throughout the winter, this will help you achieve your performance and wellness goals. Making vitamin D a priority is an investment in your long-term health, recuperation, and resilience.
