Vitamin D - the Sunshine and Immunity Vitamin!

healthy eating healthy living mindful movement resilience Apr 08, 2023

As the spring weather arrives, and we look forward to longer hours of sunlight, it’s time to ramp up our Vitamin D levels that may have waned during the winter months.

“D” is a fat-soluble vitamin, meaning you can store it in your fat and liver.  It has long been known to help the body absorb and retain calcium and phosphorus; both are critical for building bone.  Laboratory studies show that vitamin D can reduce cancer cell growth, help control infections and reduce inflammation. Many of the body’s organs and tissues have receptors for vitamin D, which suggest important roles beyond bone health.

And while we call “D” a vitamin, in fact it’s showing that as long as we have optimal levels, it actually acts more as a hormone, performing a number of critical functions on our bodies including supporting:

  • Healthy immunity
  • Healthy mood
  • Targeted support for over 2,000 genes
  • Healthy bone formation
  • Healthy glucose metabolism
  • Musculoskeletal comfort
  • Heart health
  • Healthy skin

We know that our bodies are able to manufacture vitamin D with exposure to sunlight, and yet many people are concerned about cancer risks from too much sunlight, resulting in them being deficient, especially in the winter months.

Vitamin D deficiency, causing devastating bone-softening effects, was reported as far back as the 1600s. Originally treated with cod liver oil in the 1800s, it wasn’t until the 1930s that vitamin D deficiency was discovered as the cause.  In northern climates, studies show up to 61% of Americans are vitamin D deficient, going up to 87% in winter months.

Optimal Sun Exposure

During summer months, UVB rays are strongest between 10am-2pm. For most people, 10-15 minutes of direct sunlight on unprotected skin during these hours will be enough to manufacture ~10,000-20,000 IU of vitamin D3. Get just enough sun to turn your skin slightly pink. Darker-skinned people will need more sun to optimize vitamin D levels.

From the skin, vitamin D3 (cholecalciferol) heads to the liver, where it is converted to calcidiol (25 hydroxyvitamin D). This is the form that circulates in the blood and is most accurately measured on a blood test.  From here, calcidiol heads to the kidneys, where it is converted to calcitriol (1,25-dihydroxyvitamin D), the most active form of vitamin D, which circulates to every tissue in the body.

Vitamin D and Immunity

Research shows that some immune issues are seasonal, due to seasonal variations in sunlight, which cause fluctuations in vitamin D levels.  And Vitamin D may activate genes that support an immune response to foreign entities in the body.  Pro-inflammatory cytokines may be responsible for many lasting health issues, and Vitamin D down-regulates (reduces) cytokine activity and supports healthy inflammatory response.

What about sunscreen?

For the past 25 years, sunscreens have only blocked out skin-protecting UVB, but not UVA. It was mistakenly thought that UVB rays potentially caused abnormal cell division in skin cells, so sunscreens were designed with SPF factors that reflect effectiveness of blocking only UVB rays. As it turns out, UVA rays are more abundant and penetrate deeper, making them more harmful than UVB rays!

Summer Sun Exposure

Try to regularly receive midday sun exposure between 10am-2pm in late spring, summer, and early fall, exposing as much skin as possible for 10-15 minutes if you are fair-skinned, and longer if you are dark-skinned. Remember, you’ve had enough when skin shows the first sign of a pinkish change.  

Key Food Sources of Vitamin D​​

Cod liver oil, salmon, sardines, tuna, mackerel, beef liver, egg yolks, butter, mushrooms, herring, catfish, anchovies, halibut, clams, shrimp.


Depending on sun exposure and testing, a recommended minimal vitamin D3 supplementation in the summer: would be 1,000-2,000 IU/day. (but check instructions on the label) and more in winter, up to 5,000 IU/day

And don't forget to test your levels: Test yourself in fall when levels are highest and in March when they are lowest. With those two numbers, everyone can safely calculate vitamin D supplement needs.

Home Practice This Week ~ 

It starts with awareness, without any need to change something right away, until you are ready. 

  • Take a look at what you eat each day and note how often you include Vitamin D-boosting foods.  
  • Get outside in the sunshine, even if it's only for a few minutes at a time.  Plan mid-day activities to boost exposure, being mindful of not getting too much.


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