In the northerly latitudes around the world, people are already starting to gear up for the inevitable: winter.  As our ‘to-do’ lists materialize to include the dreaded perennial tasks of cleaning gutters, raking leaves, storing patio furniture, and topping off the wood shed, we are oblivious to a tiny sunshine dependent chemical compound that also requires some timely attention.  Because as the days grow shorter, colder, and darker, there is less sun exposure, and we spend more time hibernating indoors, setting us up for vitamin D deficiency.

[quote align=”center”]The time is now fall, do you know where your vitamin D levels are?[/quote]
Sources of Vitamin D
Vitamin D Infographic - Optimum Health Fergus Ontario

Vitamin D Infographic – Optimum Health Fergus Ontario

We obtain vitamin D from both sunshine and diet.  Contrary to popular belief, the vast majority of vitamin D comes from the sun, and the amount from the diet is generally only incidental.  It is for this reason that vitamin D has been coined ‘the sunshine vitamin.’  Exposed skin synthesizes the vitamin from UVB rays from the sun.  The amount of vitamin the body is able to manufacture depends largely on the strength of the UVB rays, the amount of skin exposed, the duration of exposure, and how well the rays are able to penetrate the skin.

In food, the vitamin is found in all animal products, but in variable and relatively low amounts.  Most fruits, vegetables, and grains are poor sources.  The highest levels of the vitamin are found in: cod liver oil, fish, fortified dairy products, oysters, liver, egg yolk, processed deli meats (salami, ham, and sausage), and fortified cereals.

Vitamin D Deficiency in Canada

Insufficient levels of vitamin D, and even a frank vitamin D deficiency is much more common in Canada than most think.  The statistics are staggering.  One large scale study estimates that 70-97% of Canadians have sub-optimal levels of the vitamin (here).  Further, Statistics Canada estimates that 1.1 million Canadians have a frank deficiency (here).  Estimates of economic burden and premature death from vitamin D deficiency are equally as staggering.  Correcting vitamin D deficiency would save the Canadian health system an estimated $14 billion annually, and prevent 16% of premature deaths (here).

But why?  When we understand where the vitamin comes from, it becomes apparent.  In the winter months of northern locations not only do we tend to bundle up and limit our time outside, but the UVB rays are also much weaker.  In fact, for Canadians living between latitudes 43 to 55 degrees (roughly the entirety of populated Canada), there is a 4-5 month stretch  in the winter where UVB rays are not even strong enough to produce adequate levels of the vitamin, whether skin is exposed to sunshine or not.  Vitamin D deficiency is a greater risk in people with more pigmentation in the skin, and people using skin products that contain sunscreen, since these both block penetration of UV rays.

In addition to low exposure to weak UVB in winter months, our diets also tend to be relatively void of the vitamin.  Too few of us are consuming adequate amounts of fish, and there has been a general reduction in the amount of fortified dairy foods ingested.  Many of the foods high in vitamin D also happen to be foods that should not be consumed in high levels for various health reasons, such as processed deli meats and egg yolks.  This makes dietary changes alone an unlikely solution to the vitamin deficiency problem.

Problems Associated with Vitamin D Deficiency

The best understood action of vitamin D is its role in calcium and bone metabolism.  The vitamin stimulates the absorption of calcium through the digestive tract in to the bone, and stops the kidneys from excreting calcium in the urine.  A deficiency in the vitamin causes the body to pull calcium out of the bone, causing bone weakening, which can lead to rickets in children, and osteomalacia or osteoporosis in adults.  Less understood problems thought to be associated with low vitamin D levels include muscle pain/weakness, heart disease, multiple sclerosis, diabetes, and certain forms of cancer.   Colon cancer, breast cancer, and multiple sclerosis all have the highest world-wide instance in northerly climates with the lowest levels of light, and a vitamin D connection has been postulated.

Vitamin D and Seasonal Affective Disorder

Vitamin D deficiency has been proposed as a potential cause of season affective disorder (SAD).  SAD, or winter depression, has been long thought to be related to diminishing levels of light during winter months.  Interestingly, most people who meet the diagnostic criteria for SAD are vitamin D deficient.  A relationship also appears to exist between severity of SAD symptoms and the extent of vitamin deficiency (here).  One small study found that supplementation of vitamin D was more effective at treating SAD than the standard medical treatment of light therapy (here).

Supplemental Vitamin D

The solution to the vitamin D deficiency problem may be as simple as taking supplemental vitamin D.  Studies indicate that 2000 IU of supplemental vitamin D daily, in those without contraindications to taking the vitamin, was able to correct the deficiency in 93% of people (here).  Of course, supplemental vitamin D is not safe for everyone, and toxicity from excessive vitamin D is dangerous, causing calcification and damage to internal organs, as well as the formation of calcium kidney stones.  Always talk to your doctor about what is best for you.