Potential Effects of Vitamin D in the Body

Research suggests that a general negative correlation exists between serum vitamin D and cancer fatality [3]. Whilst theres also research into specific cancer types and potential effects of vitamin D. For example it was found that women with a sufficient vitamin D status at the time of diagnosis had lower grade and smaller breast cancer tumours [4]. Whilst other researchers have found that vitamin D status was significantly inversely associated to the incidence of colorectal cancer in under 50s and the same association was found for over 50s regarding adenocarcinoma, colon cancers and other invasive cancers [5]. However the jury is still out on the association between cancer and vitamin D, as research is yet to determine the full extent of these mechanisms, and some research indicates no association between vitamin D supplementation and cancer incidence thus greater research is required in the field [6]. 

Some researchers have also sought to determine associations between vitamin D and mood disorders. Meta-analysis found lower vitamin D prevalence in those with depression when compared to controls, and analysis of the ten cross-sectional studies found a higher odds ratio for depression in patients with the lowest vitamin D status compared to those with the highest vitamin D status. Suggesting a potential impact of low vitamin D status on the risk of depression. However, it's crucial to remember associations don't always mean a direct correlation exists between the two measures. [7]

Some research has also identified links between vitamin D status and functions of the skin barrier including alopecia and psoriasis, cognitive function and skeletal muscle strength and development. [8]

Vitamin D Absorption

Unlike many other essential nutrients, vitamin D is primarily obtained through sunlight exposure rather than food. When UVB rays from the sun reach the skin, they trigger vitamin D synthesis. However, during the winter, especially in countries located above 37 degrees latitude, UVB radiation is insufficient for adequate vitamin D production. [9]

Why Winter Poses a Challenge

From October to March, individuals living in higher latitudes produce little to no vitamin D from sunlight. This is because:

• Decreased UVB rays reaching the earth's surface - Usually affecting those who reside in regions north and south of ~33 degree latitude. [10]

• Shorter daylight hours limit outdoor exposure.

• Colder temperatures result in more time spent indoors and increased skin coverage with clothing

This seasonal reduction in vitamin D synthesis can contribute to lower serum vitamin D levels, which is why experts recommend considering alternative sources during the winter months.

How to Maintain Healthy Vitamin D Levels

1. Consider a Supplement

Public health guidelines in the UK and many other countries recommend that adults take a daily supplement of 10 micrograms (400 IU) of vitamin D between October and March [1]. Whilst most vitamin D supplements on the market are sufficient. Below are some of my favourites. 

2. Incorporate Vitamin D-Rich Foods

While diet alone may not provide sufficient vitamin D, including these sources can help:

• Oily fish (salmon, mackerel, sardines) [11]

• Fortified foods (cereals, plant-based milk, orange juice)

• Egg yolks and mushrooms [11]

• Cheese and beef liver [11]

3. Maximize Safe Sunlight Exposure

Although UVB levels are lower in winter, spending time outdoors during daylight hours can still provide benefits for overall well-being. Engaging in outdoor activities, even on overcast days, can help regulate circadian rhythms and improve mood. [12]

Who Is Most at Risk of Vitamin D Deficiency?

Certain groups are more susceptible to vitamin D deficiency, including:

• Older adults, are often at a higher risk of vitamin D deficiency often as a result of reduced mobility, leading to lower exposure to the sun. [13]

• People with darker skin, as higher melanin levels reduce UVB absorption. [14]

• Individuals who spend most of their time indoors or wear clothing that limits skin exposure [14]

A Balanced Approach

Maintaining adequate vitamin D levels in winter is a key aspect of overall health. By ensuring sufficient intake through supplementation, dietary choices, and maximising safe sun exposure, you can support your well-being throughout the colder months. If you have concerns about your vitamin D levels, consulting a healthcare professional for personalised advice can be beneficial.

Staying informed and making small, evidence-based adjustments can contribute to optimal health during winter and beyond.

Higher Nature has kindly provided a 10% discount until the end of March 2025 using the code: NF10

References

1.

NHS. Vitamin D - Vitamins and Minerals [Internet]. NHS. NHS Digital; 2020. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/

2.

Prietl B, Treiber G, Pieber T, Amrein K. Vitamin D and Immune Function. Nutrients [Internet]. 2013 Jul 5 [cited 2025 Feb 10];5(7):2502–21. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3738984/

3.

Trude Eid Robsahm, Steinar Tretli, Peter Abusdal Torjesen, Babigumira R, Schwartz GG. Serum 25-hydroxyvitamin D Levels Predict Cancer survival: a Prospective Cohort with Measurements Prior to and at the Time of Cancer diagnosis. Clinical Epidemiology. 2019 Aug 1;Volume 11:695–705.

4.

Manocha A, Brockton NT, Cook L, Kopciuk KA. Low Serum Vitamin D Associated with Increased Tumor Size and Higher Grade in Premenopausal Canadian Women with Breast Cancer. Clinical Breast Cancer. 2023 Aug 1;23(6):e368–76.

5.

Kim Y, Chang Y, Cho Y, Chang J, Kim K, Park DI, et al. Serum 25-Hydroxyvitamin D Levels and Risk of Colorectal Cancer: an Age-Stratified Analysis. Gastroenterology [Internet]. 2023 Oct [cited 2025 Feb 10];165(4):920–31. Available from: https://pubmed.ncbi.nlm.nih.gov/37429364/

6.

Manson JE, Cook NR, Lee I-Min, Christen W, Bassuk SS, Mora S, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. New England Journal of Medicine [Internet]. 2019 Jan 3 [cited 2025 Jan 4];380(1):33–44. Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa1809944

7.

Anglin RES, Samaan Z, Walter SD, McDonald SD. Vitamin D Deficiency and Depression in adults: Systematic Review and meta-analysis. British Journal of Psychiatry [Internet]. 2013 Feb [cited 2025 Feb 10];202(2):100–7. Available from: https://www.cambridge.org/core/journals/the-british-journal-of-psychiatry/article/vitamin-d-deficiency-and-depression-in-adults-systematic-review-and-metaanalysis/F4E7DFBE5A7B99C9E6430AF472286860

8.

Feldman D, Krishnan AV, Swami S, Giovannucci E, Feldman BJ. The Role of Vitamin D in Reducing Cancer Risk and Progression. Nature Reviews Cancer [Internet]. 2014 Apr 4 [cited 2025 Feb 10];14(5):342–57. Available from: https://www.nature.com/articles/nrc3691

9.

Mead N. Benefits of sunlight: a Bright Spot for Human Health. Environmental Health Perspectives [Internet]. 2008 Apr [cited 2025 Feb 11];116(4). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290997/

10.

Wacker M, Holick MF. Sunlight and Vitamin D. Dermato-Endocrinology [Internet]. 2013 Jan 1 [cited 2025 Feb 11];5(1):51–108. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897598/#:~:text=Vitamin%20D%20is%20the%20sunshine,turn%20isomerizes%20into%20vitamin%20D3.

11.

Lamberg-Allardt C. Vitamin D in Foods and as Supplements. Progress in Biophysics and Molecular Biology [Internet]. 2006 Sep [cited 2025 Feb 10];92(1):33–8. Available from: https://doi.org/10.1016/j.pbiomolbio.2006.02.017

12.

Burns AC, Saxena R, Vetter C, Phillips AJK, Lane JM, Cain SW. Time Spent in Outdoor Light Is Associated with mood, sleep, and Circadian rhythm-related outcomes: a cross-sectional and Longitudinal Study in over 400,000 UK Biobank Participants. Journal of Affective Disorders. 2021 Dec;295:347–52.

13.

Boucher BJ. The Problems of Vitamin D Insufficiency in Older People. Aging and Disease [Internet]. 2012 Jun 6 [cited 2025 Feb 11];3(4):313. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3501367/

14.

National Institute for Health and Care Excellence. Vitamin D Deficiency in Adults [Internet]. NICE. 2022 [cited 2025 Feb 11]. Available from: https://cks.nice.org.uk/topics/vitamin-d-deficiency-in-adults/background-information/causes/

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