Do You Need Extra Vitamin D During Winter?

During the winter months, there’s one nutrient in particular that typically requires a little more attention: vitamin D, sometimes referred to as the sunshine vitamin. Unlike most nutrients, the majority of our vitamin D does not come from food. It is made in the skin in response to sunlight, which means the season you are in can have an impact on how much your body can produce.

This article explores what vitamin D does, who is most at risk of having lower levels, and the practical steps that can help maintain your levels through winter.

What does vitamin D actually do?

Vitamin D is a fat-soluble vitamin that acts on several systems throughout the body.

It is best known for its role in supporting bone health - contributing to normal bone structure and the maintenance of normal teeth. Specifically, vitamin D is necessary for the normal absorption and utilisation of calcium and phosphorus. Due to this role in supporting calcium absorption, the two are often discussed together. 

Vitamin D also contributes to the maintenance of normal muscle function and to the normal function of the immune system. 

The impact of winter 

Because we rely on sunlight for most of our vitamin D rather than food, the season can have an impact on how much the body can make. The angle of the sun between about May and August, means that the UV index across much of the country stays low enough that the skin produces very little vitamin D for the majority of the day. According to a joint consensus statement from the Ministry of Health and Cancer Society of New Zealand, vitamin D deficiency is more common in late winter and early spring, and the effect is most pronounced the further south you live. 

Your body does store vitamin D for a period after summer, which carries many people part of the way through. For some, though, those stores run down before spring arrives.

Who is more likely to run low

Winter affects everyone, but some groups tend to start from a lower baseline or drop levels faster. Based on New Zealand data, you may be more likely to have low vitamin D if you:

• Live in the South Island, with the exception of the Nelson and Marlborough region 

• Have naturally darker skin, which needs more sun exposure to make the same amount of vitamin D

• Spend most of your day indoors, whether through work, mobility or simply the cold

• Cover most of your skin when outside

People who have had bariatric surgery are also more likely to run low, which is why ongoing monitoring is a standard part of post-surgical care.

How to know if you’re low in vitamin D 

Unlike some other nutrients, low vitamin D typically has no obvious symptoms. Many people with levels below the recommended range feel completely normal day to day, which is why it may go unnoticed for months.

Maintaining adequate vitamin D levels is important for bone and muscle health, but because vitamin D deficiency often presents with no symptoms, a blood test is the most reliable way to check your levels. 

Practical points for winter

A few things that may help over the colder months:

• Make the most of midday sun. Between May and August, a short period of sun on the face, hands and lower arms around the middle of the day is the most efficient window. Outside summer, the risk of overdoing UV exposure is much lower, though sun-safe habits still apply on clear days.

• Keep your supplement routine consistent. If you have been recommended to take a vitamin D supplement, winter is the time to be reliable with it. Vitamin D is absorbed best when taken with food.

• Include vitamin D foods where you can. Oily fish and eggs add a modest amount and are worth having in the rotation.

• Know your numbers. If it has been a while since your levels were checked - winter is a good time for a review.

A note of caution: vitamin D is stored in the body, and very high doses taken over long periods can cause harm. Supplementation is not always required, so it’s best to check in with your clinical team before adding in a new supplement. 

Summary

Over the New Zealand winter, the body makes far less vitamin D due to reduced sun exposure. Vitamin D is an important nutrient for bones, muscle function, and many other areas of health, and it’s important to look after levels throughout the colder months, in particular. Because low vitamin D rarely announces itself, a blood test remains the most reliable way to assess your levels and know whether you may need an additional supplement.

For Bariatric Patients 

If it has been a while since your levels were checked, a blood review through Tailor Clinics is a straightforward way to assess your vitamin D levels, alongside many other nutrients. 

Reference 

• Ministry of Health and Cancer Society of New Zealand. 2012. Consensus Statement on Vitamin D and Sun Exposure in New Zealand. Wellington: Ministry of Health.

The information in this article is general in nature and intended for educational purposes only. It is not a substitute for individualised medical or nutritional advice. Always consult your healthcare provider for guidance specific to your situation. Tailor Clinics is part of the same group as Tric Nutrition.