Vitamin D is a fat-soluble vitamin that plays a crucial role in many of the body’s functions. One of the main ways we can maintain healthy levels of vitamin D in our body is through direct sunlight on the skin. It’s even coined the name “sunshine vitamin”. However, during the winter months, especially in the northern regions, you may have limited access to sunlight which can cause concern for vitamin D deficiency which can have an impact on our bone health, mood and immunity.

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Why is Vitamin D essential?

The functions of vitamin D go far beyond what many realize, including:

Bone health

Vitamin D is essential for bone health! Adequate vitamin D levels aid in calcium and phosphorus absorption.

With chronic or severe vitamin D deficiency, low calcium levels can happen. Since vitamin D helps your body absorb calcium from food, a deficiency can lead to not getting enough calcium in your blood. This can lead to something called parathyroidism! This is where your parathyroid glands release more of parathyroid hormone (PTH) to try to raise calcium levels! Over time, too much PTH can cause issues like weak bones and kidney stones as the body tries to balance calcium. Overtime this leads to Osteomalacia (softening of bones) in adults and rickets in children.

Mood

Seasonal Depressive Disorder (SAD) is a type of depression triggered by reduced sunlight during fall and winter. Lower sunlight exposure can lead to decreased vitamin D production, which may contribute to symptoms like fatigue, sadness and low energy. Research has found a correlation between low vitamin D levels and depressive symptoms, including those seen in SAD³.

If you notice persistent feelings of sadness, fatigue or difficulty concentrating during the darker months, its important to reach out to your healthcare provider. They can evaluate your symptoms and provide tailored recommendations, which may include testing for vitamin D levels or exploring other evidenced based approaches to managed SAD.

Immunity

Your adaptive immune system is like your body’s personalized defense team. It learns to recognize and attack specific germs you’ve been exposed to like viruses or bacteria, while ignoring harmless substances. Vitamin D helps train your adaptive immune system by training immune cells like T-cells and B-cells to respond effectively without overreacting (cause inflammation or allergies) or underreacting (leading to frequent infections). For example, if you catch a cold, vitamin D can help your body fight it efficiently while avoiding unnecessary inflammation.

How Winter can Affect Your Vitamin D Levels

Typical causes of vitamin D deficiency are due to not getting enough vitamin D through food and/or through sunlight. Specifically looking at the Winter season, several factors contribute to decreased vitamin D production include:

• Less sunlight: shorter days and overcast skies reduce UVB ray exposure.
• Indoor lifestyle: We tend to spend more time indoors to escape the cold.
• Geography: People living in northern latitudes may not get enough UVB rays to produce vitamin D, even on sunny winter days.

A third possible reason for vitamin D deficiency could be due to your body not being able to properly absorb or use Vitamin D. Certain medical conditions such as Cystic Fibrosis, Crohn’s disease, Celiac disease, Obesity, Kidney and Liver disease can cause vitamin D deficiency also.

Certain medications can also lower vitamin D levels:

• Laxatives
• Steroids (such as prednisone)
• Cholesterol lowering drugs
• Seizure preventing drugs
• Rifampin (a tuberculosis drug)
• Orlistat (a weight loss drug)

Signs of Vitamin D deficiency in adults:

• Fatigue/low energy
• Bone pain
• Mood changes like depression, feelings of sadness
• Muscle weakness, muscle aches or muscle cramps

Sources of Vitamin D

Sun: As mentioned earlier, vitamin D is produced in your skin when it’s exposed to UVB rays from the sun. It is greatly influenced by quite a few factors such as¹:

• Season
• Time of day
• Latitude
• Altitude
• Air pollution
• Skin pigmentation
• Sunscreen use
• Passing through glass/plastic
• Aging

Tips: Try to get outside on a sunny winter day around midday. Areas like your arms, hands should be uncovered to absorb sun’s rays. For many though, this isn’t enough to meet needs.

Dietary Sources: Since sunlight might not suffice, vitamin D sources of food become very important.

Fatty Fish Salmon, rainbow trout, tuna and sardines are among the best natural sources. Specifically wild-caught salmon generally has higher levels of vitamin D than farmed salmons and much of the vitamin D is found close to or within the skin of the fish. For maximum benefit, cooking methods to retain the skin are baking or grilling.

Egg Yolks Depending on how the hens were raised, each egg yolk provides generally about 40 IU per yolk. Free-Range or Pasture-Raised hens produce egg yolks with higher levels of Vitamin D compared to those of caged hens, as the sunlight exposure boosts the hens’ own vitamin D production. Given there are not too many natural foods high in Vitamin D, consider choosing food and drinks that are fortified with vitamin D as recommended by the 2020-2025 Dietary Guidelines.

Dairy & Fortified Soy Alternatives

• Soy milk (unsweetened)
• Cow’s Milk
• Non-fat or low-fat plain yogurt
• Kefir
• American cheese (fortified)

Mushrooms (some) A variety of mushrooms available on the market have been treated with UV light to increase vitamin D levels. In the grocery store, look for “Vitamin D enriched” or “High vitamin D” on packaging.

Other Beverage Alternatives

• Orange juice, fortified
• Almond milk, fortified
• Rice milk, fortified

Supplements: A Vitamin D3 supplement can be a practical solution for meeting your needs in winter or all year depending on the situation.

As always, its important to consult with your healthcare provider before starting any supplementation. Assessment of vitamin D levels include consulting with your primary healthcare provider where they can order a blood test to measure your levels.

This also brings up the topic of annual physicals! Its very important to get your annual physical each year as this provides valuable insights into your health, helps to detect possible issues early, prevent future complications and keep you on track with a healthy lifestyle. Typically at your annual check up, your primary doctor will order a blood test for you and results show a picture of your metabolic health such as blood sugar, cholesterol, vitamin and mineral levels and more! If you are concerned about your Vitamin D level, make sure to request for that that test be included.

Vitamin D Toxicity

Like anything, even with vitamins, too much can affect our health in negative ways. Although vitamin D intoxication is rare it can happen when there is intentional ingestion of extremely high doses for prolonged periods of time by supplementation, not through sun exposure or diet². Vitamin D intoxication can result in negative health consequences such as hypercalcemia which is the buildup of calcium in the blood which can cause nausea/vomiting, weakness and frequent urination. One can also go on to develop bone pain and kidney problems such as the formation of calcium stones².

In conclusion…

Maintaining healthy vitamin D levels during the winter months is essential for your immune system, bone health and immunity. By incorporating vitamin D-rich foods, considering supplements and taking advantage of sunlight when you can, you’ll set yourself up for a healthier winter season.

Cold and Flu season is upon us! Click here to read lifestyle tips to help keep your immune system healthy this season!

Medical Advice Disclaimer: The information provided on this blog is for informational and educational purposes only. No material provided in this blog, including images and graphics, is intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health care provider before making any dietary changes or starting a new health care regimen.  Do not neglect professional advice because of what you may have read in this blog.

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References:

1.  Wacker, M., & Holick, M. F. (2013). Sunlight and Vitamin D: A global perspective for health. Dermato-endocrinology, 5(1), 51–108. https://doi.org/10.4161/derm.24494

2.  “Vitamin D Toxicity: What If You Get Too Much?” Mayo Clinic, https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108.

3.  Petric, Domina. (2021). The Importance of Vitamin D in Seasonal Affective Disorder and other depressive disorders. International Journal of Medical Reviews and Case Reports. 5. https://www.ejmanager.com/mnstemps/172/172-1638012350.pdf?t=1732557783.