Woman lying in the sun on the beach in a sunhat and reading a book, All About Vitamin D

Nutrition 101 – Vitamin D

Vitamin D is probably most well known for being a vitamin that our bodies can produce from sunlight. But despite it being essentially “free” for us to consume, many people are actually deficient!

Clouds, pollution, window glass, and dark skin pigmentation all decrease the amount of vitamin D our bodies can make from sunlight. Plus, depending on the intensity of the sun, for a lot of people there are many months in the year where it just isn’t strong enough for vitamin D production to take place. 

This vitamin tends to have more in common with hormones and is closely related to estrogen and cortisone. It’s actually a cholesterol-like substance and requires practically full-body participation in order to be manufactured and used.

The process starts in your skin cells as the UVB light from the sun interacts with the compound 7-dehydrochlesterol to form cholecalciferol. This new compound then heads to the liver or kidneys to be converted to 25-hydroxycholecalciferol (not the most active form) and then to the fully active form 125-dihydroxycholecalciferol by the kidneys. This is the form that we common call vitamin D3. 

The vitamin D that we consume in food or via supplements is absorbed through the intestinal wall. It’s a fat soluble vitamin, so it is absorbed along with fats and with the aid of the bile produced by our liver. The vitamin D is mainly taken to the liver for storage, but it can also be stored in our skin, brain, or bones. 


Benefits of Vitamin D

Vitamin D has a strong relationship with some of the other nutrients, especially calcium. It helps regulate calcium metabolism and aids in its absorption in the gut. It also, when needed, helps decrease the excretion of calcium by the kidneys. 

It promotes the reabsorption of calcium and phosphorus into the bones, specifically the teeth, and helps maintain a healthy blood level of calcium (and therefore pH level of the blood).  Even with adequate calcium and phosphorus intake, if there is not sufficient vitamin D levels, then these minerals will not be used effectively. 

Calcium, magnesium, and vitamin D together are very supportive of heart health and the nervous system and help prevent against osteoporosis, tooth decay, and gum disease.

Two hands holding a pile of white button mushrooms, All about Vitamin D

Depletion, Deficiency, and Toxicity

As mentioned, vitamin D production by the skin can be inhibited by pollution, clouds, the distance of the sun from the Earth, clothing, window glass, dark skin pigmentation, and sunscreen, and our bodies ability to produce vitamin D decreases naturally as we age.

A severe vitamin D deficiency disease is known as rickets which results in symptoms mainly affecting bone structure and development such as 

  • Soft skull bones and bone fragility

  • A bowing of the legs

  • Spinal curvature

  • Increased size of joints

  • Muscle spasms

  • Poor teeth structure

  • Near sightedness

  • Loss of hearing

Vitamin D is potentially one of the vitamins where it is the most easy to consume a toxic dosage. This can easily occur with either a too large supplementation dosage, and/or in combination with excessive sun exposure. It’s possible that some symptoms of sun-poisoning can be attributed to vitamin D toxicity. 

 An excessive intake of Vitamin D can show up in symptoms like:

  • Excessive thirst

  • Diarrhea

  • Nausea

  • Weakness & headaches

  • Increased levels of calcium and phosphorus in the urine


Dietary Sources of Vitamin D

Unfortunately, there aren’t a lot of foods that have vitamin D. The easiest way to eat your requirements is through seafood, but there are also a few other choices as well. Not mentioned on the list, but to be considered, is that a lot of processed foods (milk from the grocery store, cereals, and even orange juice) have been fortified with vitamin D, which would count towards your required needs. There are the main food sources of vitamin D:

  • Mushrooms

  • Milk

  • Egg yolks

  • Butter

  • Liver

  • Oily fish (mackerel, salmon, herring, sardines)

  • Cod liver oil

Sensible sun exposure will also allow your body to produce some vitamin D, of course it is hard to gauge how much is being produced at any time.

In general, aim for around 10-15 minutes of sun on exposed arms, legs, or abdomen a day (the skin shouldn’t begin turning pink – if it does you’ve gone for too long!). If you have sensitive skin, start slowly with only a couple minutes and gradually increase. 

The general aim for intake of vitamin D (through food and supplementation combined) is 600 IU per day, going up to 800IU for people over 70 years of age, and staying below a maximum intake of 4000 IU per day. (1)

(1) https://www.dietitians.ca/getattachment/464f3006-0bb2-4f1a-a338-0b21d148bacb/FACTSHEET-Food-Sources-of-Vitamin-D.pdf.aspx

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