Winter Necessity: Why Is Vitamin D Crucial for Winter Health?

Winter Necessity: Why Is Vitamin D Crucial for Winter Health?

Often referred to as the "sunshine vitamin," vitamin D is essential for various bodily functions, particularly for maintaining a robust immune system. However, with limited sunshine, frequent rain, and increased darkness during the winter months, our bodies have fewer opportunities to produce this crucial vitamin.

So, how can we ensure we get the necessary amounts of vitamin D in winter? And how do we know if we're getting enough?

Read on to discover why vitamin D is vital for immune function, how it's produced in the body, the best sources of vitamin D, the effectiveness of supplements, and more about the overall benefits of this essential nutrient.

How Does Vitamin D Help the Body?

Vitamin D plays several critical roles in maintaining health:1-3

  1. Bone Health: It facilitates calcium absorption in the gut and maintains proper calcium and phosphate levels, crucial for strong and healthy bones.
  2. Immune Function: Vitamin D supports the immune system by enhancing the infection-fighting capabilities of monocytes and macrophages, while also reducing inflammation to help lower the risk of infections.
  3. Muscle Function: It aids in muscle function and strength, and thereby reducing the risk of falls and fractures in older adults.
  4. Mood and Mental Health: There is evidence suggesting that vitamin D can help regulate mood, which is particularly beneficial during the darker winter months.

The Immune Benefits of Vitamin D

Vitamin D is particularly important for immune function. Studies have shown that individuals with adequate vitamin D levels are less likely to suffer from infections such as colds and flu.4,5

In fact, vitamin D has been found to reduce the risk of respiratory infections,6 which is particularly relevant during the winter months when such infections are more prevalent.

Sources of Vitamin D for the Body

Vitamin D is unique because it functions both as a nutrient we consume and a hormone our bodies produce. The most significant source of vitamin D is sunlight, which triggers its production in the skin through the action of UVB rays on an oily substance called ergosterol.

But what can we do to obtain vitamin D when the sun isn't shining?

Besides sunlight, we can get vitamin D from various foods such as halibut fish oil, cod liver oil, sardines, tuna, butter, sunflower seeds, and eggs. For those tested and found to be deficient, supplements are also an effective option.

When the sun is shining, take advantage by exposing your skin for 5-15 minutes daily, preferably between 10 am and 3 pm. Those with darker skin may need more time to produce adequate vitamin D.7,8

Causes of Vitamin D Deficiency and Risks

During the winter months, the angle of the sun's rays and shorter daylight hours significantly reduce our skin's ability to produce vitamin D. Additionally, people tend to spend more time indoors and wear more clothing, further decreasing sunlight exposure. Several other factors contribute to vitamin D deficiency:1,7,9

  • Geographic location: People living further from the equator have less UVB exposure, especially in winter.
  • Skin pigmentation: Melanin reduces the skin’s ability to produce vitamin D, putting individuals with darker skin tones at a higher risk.
  • Age: Older adults have reduced skin thickness and may produce less vitamin D.
  • Diet: Limited intake of vitamin D-rich foods can contribute to deficiency.
  • Obesity: Higher body fat levels can store vitamin D, making it less bioavailable.

Ideal Levels of Vitamin D 

The optimal levels of vitamin D are measured in either nanomoles per litre (nmol/L) or nanograms per millilitre (ng/mL). One nmol/L is equal to 0.4 ng/mL. For general health, recommended levels for children and adults are:8,10,11

  • 50-100 nmol/L (20-40 ng/mL)

Maintaining these levels can help support bone health, immune function and overall wellbeing.

A blood test, with your GP, is the way to determine your vitamin D status.

Are Vitamin D Supplements Effective?

Vitamin D supplements can be an effective way to correct deficiency and ensure adequate intake, especially during the winter months when sunlight exposure is limited. 

Supplements come in two forms: D2 (ergocalciferol) and D3 (cholecalciferol). Research suggests that D3 is more effective at raising and maintaining adequate vitamin D levels in the blood.12,13

When taking supplements, it's essential to follow the recommended dosage and consult with a healthcare provider, as excessive intake can lead to toxicity.

Always consult with a healthcare professional before starting any new supplement regimen to ensure it’s right for you.

Interested in learning more? For more information on the science behind magnesium, sign-up to our monthly e-newsletter,  or read more great articles from Micronutrition.

 

This article was written by Stephanie Berglin, Nutritionist and Herbalist.

 

References:

  1. Healthdirect. Vitamin D and your health. Healthdirect Australia 2024, https://www.healthdirect.gov.au/vitamin-d-and-your-health
  2. Zmijewski MA. Vitamin D and human health. Int J Mol Sci 2019;20(1):145.
  3. Bikle DD. Vitamin D: Production, metabolism and mechanisms of action. [Updated 2021 Dec 31]. In: Feingold KR, Anawalt B, Blackman MR, et al., editors. Endotext [Internet], https://www.ncbi.nlm.nih.gov/books/NBK278935/
  4. Zhu Z, et al. Association between vitamin D and influenza: Meta-analysis and systematic review of randomized controlled trials. Front Nutr 2022;8:799709.
  5. Grant WB, et al. Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths. Nutrients 2020;12(4):988.
  6. Charoenngam N, Holick MF. Immunologic effects of vitamin D on human health and disease. Nutrients 2020;12(7):2097.
  7. SunSmart. UV and vitamin D. Cancer Council Victoria 2024, https://www.sunsmart.com.au/uv-radiation/uv-and-vitamin-d 
  8. Health Professionals Clinical Practice Guidelines. Vitamin D deficiency. The Royal Children’s Hospital Melbourne 2024, https://www.rch.org.au/clinicalguide/guideline_index/Vitamin_D_deficiency/ 
  9. Better Health Channel. Vitamin D. Department of Health, State Government of Victoria 2024, https://www.betterhealth.vic.gov.au/health/healthyliving/vitamin-d#rpl-skip-link
  10. Office of Dietary Supplements (ODS). Vitamin D fact sheet for consumers. National Institutes of Health (NIH) 2022, https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
  11. Eatforhealth.gov.au. Vitamin D. Nutrient Reference Values for Australia and New Zealand, Australian Government 2024, https://www.eatforhealth.gov.au/nutrient-reference-values/nutrients/vitamin-d
  12. van den Heuvel EG, et al. Comparison of the effect of daily vitamin D2 and vitamin D3 supplementation on serum 25-hydroxyvitamin D concentration (total 25(oh)d, 25(oh)d2, and 25(oh)d3) and importance of body mass index: A systematic review and meta-analysis. Adv Nutr 2024;15(1):100133.
  13. Alayed Albarri EM, et al. Effectiveness of vitamin D2 compared with vitamin D3 replacement therapy in a primary healthcare setting: a retrospective cohort study. Qatar Med J 2022;2022(3):29.

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