Vitamin-D: Is It Affecting Your Performance, Immunity & Well-being?

Vitamin D has had my attention for just over 6 years. With the birth of my first daughter, I supplemented her with it that first cold and dreary winter – taking the recommended daily dose (RDA) when spending less time outside seemed to make sense for me. At the time, my basis for supplementation was rooted in its benefits for the immune system. Babies are challenging enough without a cold!

What I knew was vitamin D deficiency predisposes children to respiratory infections and vitamin D3 supplementation during the winter may reduce the incidence of contracting influenza (aka the flu! ).

So, I decided to do a little more research after that winter to see if this claim, among others, were scientifically sound or just something that was said among users further enhancing the placebo effect.  What I found was justification in adding this supplement and vitamin-D rich foods to my families daily routine as well as some other interesting new research I’d like to share.

Vitamin-D Basics

What Is It?

Vitamin D is a fat-soluble (dissolve in fat and are stored in fat throughout the body) vitamin that is naturally present in very few foods. It’s added to many foods such as cereal and milk products, and available as a dietary supplement either alone or in products such as fish oil. It is also produced in the body when ultraviolet (UV) rays from the sun strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements must undergo two transformation in the body for us to use it. The first occurs in the liver and the second occurs primarily in the kidney. Nearly every tissue and cell in our body has a vitamin D receptor. Without enough activated vitamin D in the body, dietary calcium cannot be absorbed. Calcium is also essential for signaling between brain cells, development of bone, and tooth formation.


Why Is It Important?

For us living in colder climates, vitamin-D from UV radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as do foods containing vitamin D. Hooray!

But what else? The list of vitamin D’s benefits are quite impressive and enough to motivate you off the couch and outside to reach your daily dosage and ounce of supplement prevention! They include:

  •  promotes calcium absorption in the gut
  • maintains adequate serum (blood) calcium and phosphate concentrations to promote bone growth
  • prevents rickets in children and “softening of the bones” in adults
  • together with calcium, vitamin D also helps protect older adults from osteoporosis
  • modulation of cell growth,
  • neuromuscular and immune function
  • reduction of inflammation
  • high doses of vitamin D taken one hour after sunburn significantly reduce skin redness, swelling, and inflammation
  • increase performance (see below)
  • improved sleep quality

Some research suggests that adequate vitamin D may have other benefits, such as:

  • lowering the risk of breast cancer
  • lowering the risk of colorectal cancer
  • lowering the risk of cardiovascular disease in men
  • lowering the risk of multiple sclerosis

Effects On Performance

“There is strong correlation between vitamin D sufficiency and optimal muscle function.” (11)

Many studies that I found kept concluding the same thing. It wasn’t surprising considering the many roles it has in the body. Imagine the following implications and being deficient in this vitamin? Imagine what it could do for an athlete once they discover their levels through testing and choose to correct it through foods and/or supplementation?

Increasing serum (blood) levels of vitamin D:

  • reduce inflammation
  • reduce pain, and
  • myopathy

while increasing;

  • muscle protein synthesis
  • ATP concentration
  • strength
  • jump height, jump velocity, jump power
  • exercise capacity
  • physical performance

Optimal musculoskeletal benefits occur at levels above the current definition of sufficiency (> 30 ng/mL) with no reported sports health benefits above 50 ng/mL.


  “Vitamin D deficiency is common in athletes. For athletes presenting with stress fractures, musculoskeletal pain, and frequent illness, one should have a heightened awareness of the additional likely diagnosis of vitamin D deficiency. Correction of this deficiency is completed by standardized and supervised oral supplementation protocols producing significant musculoskeletal sports health benefits.” (11)


Low-D Implications

About 40% of Canadians were below the RDA value in winter, compared with 25% in the summer. Here are a few implications I came across in my research:

  • Increased risk of cancers
  • Higher blood pressure
  • The development of neurological disorders
  • The development of diabetes
  • Increased loss of muscle strength and mass as we age
  • Lower levels of immunity
  • Weakened immune system
  • Seasonal depression
  • Autoimmune disease
  • eczema and psoriasis
  • Dementia

Factors For Low Vitamin D


“But I have a corner office with floor to ceiling windows and I don’t use a sun visor on my drive home, so I’m good right?!”

Nope. Glass blocks virtually all UVB, preventing vitamin D from being made. A great reason to turn off the A/C and roll down the window! And people on low fat diets and those taking steroids and weight loss medications may be at risk too. During the winter, very little UVB reaches us, and thus, less cholesterol is used to synthesize vitamin D in the body. This is one of the reasons blood cholesterol levels may be higher during the winter months.

Below are some insights as to why we might be low or deficient of vitamin D.

Location: The further away from the Equator you live, the less vitamin D–producing UVB light reaches the earth’s surface during the winter. Short days and clothing that covers the body during this time also limit UVB exposure.

Pollution: Carbon particles in the air from the burning of fossil fuels, wood, and other materials scatter and absorb UVB rays, diminishing vitamin D production. In contrast, ozone absorbs UVB radiation, so pollution-caused holes in the ozone layer could end up enhancing vitamin D levels.

Genetics: Melanin is the substance in skin that makes it dark. It “competes” for UVB with the substance in the skin that kick-starts the body’s vitamin D production. As a result, dark-skinned people tend to require more UVB exposure than light-skinned people to generate the same amount of vitamin D.

Bodyweight: Body fat sops up vitamin D, so it’s been proposed that it might provide a vitamin D rainy-day fund: a source of the vitamin when intake is low or production is reduced. But studies have also shown that being obese is correlated with low vitamin D levels and that being overweight may affect the bioavailability of vitamin D.

Age: Compared with younger people, older people have lower levels of the substance in the skin that UVB light converts into the vitamin D precursor. There’s also experimental evidence that older people are less efficient vitamin D producers than younger people.

Poor Diet: Read the food list below and/or start supplementing. Consult your doctor for blood testing.


“Recommended” Daily Allowances And Ranges For Bloodwork

Recommendations all have to start somewhere and that somewhere in 2011 was Health Canada’s daily recommended intakes for vitamin D to be at 400 international units (IU) for infants, 600 IU for children aged one to adults aged 70, and 800 IU for adults over 70.

The Big Vitamin D Mistake

Now consider this PubMed article from July 2017.

“…we call public health authorities to consider designating as the RDA at least three-fourths of the levels proposed by the Endocrine Society Expert Committee as safe upper tolerable daily intake doses. This could lead to a recommendation of 1000 IU for children <1 year on enriched formula and 1500 IU for breastfed children older than 6 months, 3000 IU for children >1 year of age, and around 8000 IU for young adults and thereafter. Actions are urgently needed to protect the global population from vitamin D deficiency.

  The Authors want to raise your RDA vitamin-D levels as an adult from 600IU to 8000IU!

Health Canada also advises year-round vitamin D supplementation for all Canadian adults. In a press release dated March 17, the American researchers stated that their work showed the current RDAs for vitamin D are “only about one-tenth those needed to cut incidence of diseases related to vitamin D deficiency.” – as seen above.

Now sinks in the importance of vitamin-D supplementation!

How Do I Know If I’m Deficient?

People who have vitamin D blood levels at or above 50 nmol/L are considered to have aqequate vitamin D levels. A simple blood test can confirm this through your doctor. But if you have lower than 50 nmol\L you are considered to be below the cut-off for optimal levels and you should take steps to increase your levels through natural and/or supplementation means. Lastly, some people with vitamin D blood levels (serum) between 30 and 50 nmol/L are potentially at risk of inadequacy relative to bone health.


Food & Supplementation

Aside from slathering on the tanning oil by the pool or walking around in December in your favourite muscle shirt, supplementing in the winter months should be mandatory.

There are 2 types you can take. The animal form is vitamin D3 and the plant form is vitamin D2.  Both vitamin D2 and D3 seem to be effective at maintaining blood levels (serum) of vitamin D in the body. Look for a product that delivers at least 1000 IU a drop and hit your daily goal.

Some examples of vitamin-D sources from food include:

  • Fish/Cod liver oil
    1 tsp: 440 IU (over 100% DV)
  • Sardines
    3 ounces: 164 IU (41% DV)
  • Salmon
    3 ounces: 400 IU (100% DV)
  • Mackerel
    3 ounces: 400 IU (100% DV)
  • Tuna
    3 ounces: 228 IU (57% DV) 
  • Raw Milk
    1 cup: 98 IU (24% DV)
  • Caviar
    1 oz: 33 IU (8% DV)
  • Eggs
    1 large: 41 IU (10% DV)
  • Mushrooms
    1 cup: 2 IU (1% DV)

…and more options for vegetarians:

  • ricotta cheese
  • cereals
  • orange juice
  • oatmeal
  • butter
  • white mushrooms







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