The Sunshine Vitamins: A Guide to a Brighter Winter

29 Jan

As the dark, cold days of January and February set in, many people experience a dip in their mood and energy. For some, this manifests as Seasonal Affective Disorder (SAD), a type of depression that comes and goes in a seasonal pattern. While the lack of sunlight is a well-known culprit, its impact on a crucial nutrient, vitamin D, is significant. This article explores the science behind vitamin D, its vital partnership with vitamin K, and how to ensure you're getting enough to support your physical and mental well-being during the UK's darkest months.

Why Vitamin D is Non-Negotiable

Vitamin D, often called the "sunshine vitamin," is a fat-soluble hormone that our bodies produce when our skin is exposed to ultraviolet B (UVB) rays from the sun. It plays a fundamental role in our health, most notably by regulating calcium and phosphate absorption, which is essential for maintaining healthy bones, teeth, and muscles. Without enough vitamin D, children can develop rickets, a condition that causes soft, weak bones, while adults can suffer from osteomalacia, which leads to bone pain and tenderness.

Beyond bone health, emerging research highlights vitamin D's role in immune function, reducing inflammation, and even protecting against certain diseases. However, for those of us in the UK, relying on the sun for vitamin D is challenging. From October to early March, the sun is not strong enough at our latitude for our bodies to produce the vitamin D we need. This puts a large portion of the population at risk of deficiency.

Recognising this, the National Health Service (NHS) recommends that everyone in the UK consider taking a daily vitamin D supplement containing 10 micrograms (400 IU) during the autumn and winter months.

Beating the Winter Blues: Vitamin D and Seasonal Affective Disorder

The connection between winter and low mood is not just anecdotal. A growing body of evidence links low vitamin D levels to a higher risk of depression, including SAD. The biological plausibility of this connection is strong: Vitamin D receptors are found in brain regions that regulate mood, and the vitamin is involved in the production of key neurotransmitters such as dopamine and serotonin.

A 2014 meta-analysis published in the journal Nutrients provided compelling evidence for this link. The researchers analysed 15 randomised controlled trials (RCTs) and found that, in studies without significant biological flaws, vitamin D supplementation led to a statistically significant improvement in depression. The effect size was even comparable to that of some antidepressant medications. While more research is always needed, these findings suggest that maintaining adequate vitamin D levels is a simple, low-risk strategy for supporting mental health during the winter.

The Dynamic Duo: Why Vitamin K is Vitamin D's Best Friend

While vitamin D is crucial for absorbing calcium, its job is only half done. This is where vitamin K, another fat-soluble vitamin, comes into play. Vitamin K acts as a

director, ensuring that the absorbed calcium is deposited in the right places, our bones and teeth, and not in our arteries and soft tissues, where it can be harmful.

Vitamin D promotes the production of several vitamin K-dependent proteins, such as osteocalcin and matrix Gla protein (MGP). These proteins are inactive until vitamin K carboxylates them, essentially switching them on. Osteocalcin helps bind calcium to the bone matrix, while MGP prevents calcium from accumulating in blood vessels, a process known as vascular calcification, which is a major risk factor for cardiovascular disease.

Human studies have demonstrated the power of this synergy. A Norwegian study found that older adults with low levels of both vitamin D and vitamin K had a significantly higher risk of hip fractures, an odds ratio of 7.6, compared with those with adequate levels of both. Another large study, NOREPOS, followed over 1,300 older adults for more than eight years and found that low levels of vitamin D and K were associated with a 41% higher risk of hip fractures. These findings strongly suggest that for optimal bone and cardiovascular health, we need to consider both vitamins together.

Dietary Sources of Vitamins D and K

While supplementation is a reliable way to get vitamin D during the UK winter, we can also boost our intake through diet. Similarly, vitamin K is readily available in many common foods.

For vitamin D, oily fish are among the best natural sources. A single serving of salmon can provide a significant portion of your daily needs. Many foods in the UK are also fortified with vitamin D, including breakfast cereals and most plant-based milks. For vitamin K, the story is twofold. Vitamin K1 is abundant in green leafy vegetables like spinach and kale. Vitamin K2, which some research suggests is more effective for bone and cardiovascular health, is found in fermented foods. Natto, a Japanese dish of fermented soybeans, is by far the richest source of K2, but some hard cheeses and sauerkraut also contain it.

Vitamin D

Oily fish (salmon, mackerel, sardines): Salmon (3oz): 570 IU
Cod liver oil: 1 tbsp: 1,360 IU
Egg yolks: 1 large egg: 44 IU
Fortified foods (milk, cereals, plant milks): 1 cup fortified milk: ~120 IU
UV-exposed mushrooms: ½ cup: 366 IU
Vitamin K
Vitamin K1: Green leafy vegetables (kale, spinach, broccoli), Cooked spinach (100g): 525 mcg
Vitamin K2: Fermented foods (natto, some cheeses, sauerkraut), Natto (100g): 850-1,000 mcg

A Holistic Approach to Winter Wellness

Navigating the UK's winter months requires a proactive approach to health. The evidence is clear that vitamin D plays a crucial role in both our physical and mental well-being, and insufficient sunlight puts many of us at risk of deficiency. Supplementing with 10 micrograms (400 IU) of vitamin D daily is a simple and effective measure for most people.

To get the most out of your supplement, timing and method matter. As a fat-soluble vitamin, research shows that taking your vitamin D supplement with a meal containing fat can increase absorption by over 30% compared to taking it on an empty stomach. The good news is that the type of fat doesn't seem to make a difference, so a meal with healthy fats like avocado, nuts, or olive oil is an excellent choice.

When it comes to the form of the supplement, be it a traditional tablet, capsule, or oral spray, the evidence suggests that all are effective for most people. While sprays are often marketed as having superior absorption, a systematic review of studies found that oral sprays are an equally effective alternative to capsules, not necessarily better. Sprays can, however, be a great option for individuals who have difficulty swallowing pills or have certain malabsorption issues. Ultimately, the best method is the one you will take consistently, so choose the form that best suits your personal preference and lifestyle.

However, to truly maximise the benefits, we must also consider vitamin K. This essential partner ensures that the calcium mobilised by vitamin D is used to strengthen our bones rather than harm our arteries. When choosing a supplement, opt for vitamin D3 (cholecalciferol) rather than vitamin D2 (ergocalciferol). A comprehensive meta-analysis of randomised controlled trials found that vitamin D3 is significantly more effective at raising and maintaining serum vitamin D levels than D2, making it the superior choice for supplementation. You can get combined supplements to make this easier, and by combining sensible supplementation with a diet rich in oily fish, leafy greens, and fermented foods, we can build a robust foundation of health to carry us through the winter and into the brighter days of spring.

As always, discuss these options with your G.P. or medical professional to ensure you get the best results. Having blood tests either through the NHS, if you can, or privately will give the most accurate picture.