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Vitamin D: for bones, immunity, mood, sleep, and more!

Updated: Jan 31


Vitamin D is important in over 400 body systems, and has been in the spotlight recently for supporting immunity during the Covid pandemic.


Yes, Vitamin D is critical for bone health, and it benefits bones in more ways than one:

  • without Vitamin D, the body can only absorb 10-15% of dietary calcium, important in bone formation and bone density

  • it escorts calcium into the bones

  • a recent metanalysis concluded that Vitamin D and calcium, taken together, may help prevent falls in the elderly


Immune support: Studies show that low levels of Vitamin D3 were significantly associated with severity of infection and risk of death due to COVID-19 disease. People with low levels of Vitamin D, who supplemented when they had been diagnosed with Covid, had less severe disease and recovered faster. And of course Covid isn’t the only infection we want Vitamin D to help us fight, just the most recent one.


Mood modulation, especially in dark winter days. SAD is short for seasonally affective disorder. People with SAD tend to depression during dark months, and feel better when they spend time by full spectrum lights, or take Vitamin D. We don’t know whether the benefit of full spectrum light is solely due to the light boosting their Vitamin D levels.

Sleep: Clinical studies show that low levels of Vitamin D are associated with a higher risk of sleep disorders such as poor quality and short sleep duration. Vitamin D may regulate the sleep-wake cycle, but this has not yet been broadly researched.

Inflammation: Vitamin D helps modulate inflammation in the immune response by regulating production of inflammatory cells called cytokines (see our “Short course on Long Covid” for more about these). This is probably why higher levels are associated with less risk of acute infections and fewer bad outcomes of those infections. There is also a tendency for people with low Vitamin D levels to suffer more from chronic inflammatory diseases, such as atherosclerosis-related cardiovascular disease, asthma, inflammatory bowel disease, chronic kidney disease, and nonalcoholic fatty liver disease, among others.

Making your own Vitamin D is a multi-step biochemical process. First, sunlight on your skin triggers cholesterol present in your skin to change structure. This is transported to be activated in your liver, then in to your kidneys for further activation, and only then is Vitamin D ready to be used all over the body.

Hence its nickname: “The Sunshine Vitamin”

Surprisingly, Vitamin D is actually a hormone rather than a vitamin. We just didn’t know that when it was first discovered and named. The definition of a hormone is a body chemical that is produced in one part of the body, which then has action in other cells of the body. Since every cell of your body needs Vitamin D, it fits this definition!

Supplements are generally the Vitamin D3 form, as it raises blood levels better than Vitamin D2. Vitamin D3 still needs some conversion in your body to make the active form.

How much Vitamin D to take depends on a number of factors:

  • How sunny are your days, and how much time do you spend in the sun? It has been said we need 30 minutes of sun exposure to 80% of our skin every day, to make adequate Vitamin D. And in Canada in winter, we make none: the sunlight is too weak, due to its low angle in the winter sky.

  • People who spend most of their time indoors, who cover their skin with sunscreen, or who veil their bodies when outdoors, will need to take more Vitamin D than people who love to tan

  • How dark is your skin tone? People with lighter skin make Vitamin D more readily. Those with skin that is darker are better protected from sunburn, but make less Vitamin D.

The only reliable way to know your Vitamin D level is by blood testing.

Our experience, from testing the blood levels of our patients, is that the recommended daily allowances of 400 – 800 IU are not adequate for optimal Vitamin D levels, especially if you live as far north as we do in Canada. You may have heard that too much Vitamin D can be harmful. Recent studies have shown that this is extremely rare from normal oral supplementation.

Vitamin D doses are usually stated in IU, meaning International Units, but some countries use micrograms: 1,000 IU is 25 micrograms. Most pale-skinned people do quite well with 1000 IU in summer, and 2,000 IU or more in winter, but this can vary significantly from person to person, and this is why:

A small proportion of people have genetic variations that reduce the amount of Vitamin D they can make. They often find that their blood numbers are very low, and they feel so much better after supplementing with Vitamin D. The rest of us may not feel the benefits from taking our Vitamin D, as they are less immediate and more general. These may include improved immunity leading to fewer illnesses, quicker recovery from the ones we do catch, and better bone density reducing the tendency to fracture if we fall.

People whose kidney or liver function is significantly compromised may not be able to perform the chemical activation necessary to make Vitamin D. If your kidney or liver function is significantly below par, or if you notice that dark days really affect your mood, a Vitamin D blood test is advisable. You will have to pay for the test in most countries: it isn’t usually covered. If the results are low, you have a cost-effective way of boosting your health: take Vitamin D!

Food sources: Vitamin D is a fat-soluble vitamin, so it is only found in animal foods with fat, such as cod liver oil (the richest food source), cold water fish, and eggs. It is almost impossible to get enough Vitamin D just from your diet.

So take your Vitamin D, especially in winter. You will be healthier and happier for it!

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