Vitamin D is known as the ‘sunshine vitamin’, meaning it’s hard to come by in winter. Vitamin D deficiency affects an estimated 1 billion people and poses various health risks. Supplementing vitamin D in winter is a good way to overcome deficiency, but it’s important to understand how it works to ensure we do it effectively and to avoid any negative effects.

Since vitamin D has attracted a lot of attention in recent years for its role in immune health, we’ll be delving into some of the cutting-edge research that can help you understand the importance of maintaining your vitamin D levels. We’ll discuss how seasonal variation and location affect vitamin D levels, how deficiency impacts health, and the importance of personalising supplementation.

The sunshine vitamin

Vitamin D is incorrectly labelled as a vitamin. In fact, it’s a hormone that UVB radiation from the sun triggers the skin to produce. Vitamin D consumed via food or supplements requires activation by our organs for it to be effective in our bodies. In contrast, vitamins are essential nutrients that support our health. Vitamins are not produced in our bodies and must be obtained from our diets.

Sun exposure is very important to maintaining healthy vitamin D levels. So, an article in Nutrients looks at how seasonal and geographical variation affect vitamin D production.

Seasonal and geographical variation

The authors note a previous study that found 40% of the European population were vitamin D deficient and 13% were severely deficient. For their study, they examined analysed data from 46 capital cities in Europe over an 18-year period.

The article highlights the obvious factors that sun exposure was highest in June/July and lowest in December, with lots of daily variation in summer due to cloud cover.

However, the most striking points were the variations across the continent. Winter levels of reduced sun exposure ranged from lasting 4 days in Nicosia, Cyprus, to 187 days in Oslo, Norway, and a staggering 215 days in Reykjavik, Iceland.

They found that latitude was the most important factor, as it relates to the angle the sun enters the atmosphere. The higher the latitude, the lower the radiation and amount of potential vitamin D we can produce.

How vitamin D deficiency affects you

The article in Nutrients shows the drastic variations in sun exposure between countries. That’s why it’s very important you look at what your national guidelines are for supplementation vitamin D, if necessary, and/or speak to a professional for advice.

A perspective in Foods considers vitamin D’s role in athletes’ performances. They summarised research demonstrating a direct relationship between vitamin D levels and performance parameters, including velocity, jump height, and muscle tone and force. Moreover, they noted more instances of injuries with lower vitamin D levels.

Their research indicates that having adequate vitamin D levels in your body contributes to your athletic performance and health generally.

Symptoms and risk factors for deficiency

Vitamin D deficiency occurs when the body does not get enough vitamin D from converting sunlight or from diet. Here are some of the main symptoms to watch out for:

• Frequent illness or infections.
• Fatigue and tiredness.
• Bone and back pain.
• Depression.
• Impaired wound healing.

Deficiency is commonly defined as blood levels below 20 ng/mL and insufficient levels as 21‒29 ng/mL, though these figures can vary.

Here are some of the risk factors that make you prone to vitamin D deficiency:

• Being older.
• Being overweight or obese.
• Not eating enough fish or dairy.
• Living far from the equator or in regions with little year-round sunlight.
• Staying or working indoors and working nights.

Because excessive sun exposure can cause skin cancer, sunscreen is increasingly being used for protection. Sunscreens help to reduce skin damage and cancer risk from sun exposure, but they also decrease the skin’s ability to produce vitamin D.

Supplementing vitamin D

Supplementing vitamin D is a relatively cheap and easy option to ensure that you have adequate vitamin D levels when UVB radiation isn’t sufficient. Although, understanding how much to supplement is not very straightforward.

An article in Nutrients compares the effectiveness of individualised versus standardised supplementation in athletes. In the study, a subset of athletes with vitamin D deficiency were given either individualised or standardised dosages of supplements over 10 weeks. The individualised doses were determined using a formula based on body weight and blood tests.

The importance of personalised vitamin D supplementation

The individualised group had significantly higher vitamin levels than the standardised group. This shows that a personalised approach is more effective than a one-size-fits-all approach when supplementing.

There are clearly multiple factors that affect your exposure to UVB radiation and potential for producing vitamin D without supplementation, like seasonal and geographic variation.

Risks of over-supplementing vitamin D

It is important to keep in mind that supplementing too much vitamin D can pose significant health effects. This comes from ingesting large amounts over extended periods of time and can lead to issues related to the build up of calcium in the body.

Watch out for these symptoms:

• Nausea.
• Increased thirst and urination.
• Poor appetite.
• Constipation.
• Weakness.
• Confusion.
• Ataxia: impaired balance and coordination.

Your guide to supplementing vitamin D in winter

For guidance about what amount of vitamin D you may need to supplement in winter, look for national guidelines or speak to a professional for advice.

You should see a doctor if you have any of the risk factors mentioned above and/or notice any of the symptoms of vitamin D deficiency. You can perform at-home blood tests or ask a medical professional to assist you.

Helping you to fight the winter blues

To summarise, having adequate vitamin D levels is important for immune health and maintaining multiple crucial functions in the body. Our bodies primarily produce vitamin D from our skin being exposed to direct sunlight. However, there are various reasons that we may not be getting enough sun exposure.

Supplementing vitamin D can help you to retain adequate levels despite these factors. Dosages should be personalised to suit your needs and to avoid any negative effects.

We’re interested in helping you to stay healthy all year round. So, to help guide you through the winter months, we’re providing information on how best to stay happy and healthy. Why not start with Why do we get SAD During Winter? if you want to learn more.