Vitamin D has gotten a lot of attention over the past decade, and for good reason.  This fat-soluble vitamin is made by our bodies and can be eaten or taken as a supplement.  Like all other vitamins, it is no magical cure-all, but it does play a vital role in our overall health and functioning.  Like flavonoids and vitamin A, vitamin D can and does influence the activity of our DNA, turning genes on and off by binding to receptors on the outer layer of our cells.  

Let’s dive in, shall we?

What is Vitamin D?

As mentioned above, vitamin D is a fat-soluble vitamin.  It is created in multiple steps in our bodies.  First, when skin cells are exposed to UVB radiation, a vitamin D precursor molecule is created.  This molecule travels through our blood to the liver where the next step in metabolism takes place, producing the form of vitamin D we measure with blood tests.  Finally, once this new molecule reaches our kidneys, the active form of vitamin D is created.  There is some creation of the active form of vitamin D in other cells, but the majority is made in the kidneys. 

What does Vitamin D do?

Once in its active form, vitamin D plays many important roles in the body; most are only just now being understood.  As we continue to investigate, more functions may be found - this is true for all nutrients.  Remember, science is the act of asking and investigating questions, and we work with the best available information and update as we learn more.  

Bone Health: 

One of the best understood roles of vitamin D is in bone health.  When children are deficient in vitamin D, they develop rickets, a disease of soft and weak bones that do not fully support the weight of the child’s body.  In addition to the changes in bone structure, children with rickets tend to grow very slowly, suffer from fatigue, and endure muscle and bone pain.  In adults, low vitamin D can create a condition called osteomalacia.  Osteomalacia causes many of the same symptoms of rickets without the delayed growth as growth has already ceased. 

Vitamin D exerts these effects on our bones by regulating how much calcium and phosphorus is found within our bone tissue and our blood.  Think of our bones as a storage site for these minerals.  Vitamin D helps us move calcium and phosphorus into our blood for use in cell functions or into our bones ensuring the healthiest balance possible.  If we are not consuming enough calcium or phosphorus, Vitamin D helps us move them into our blood to keep our nervous systems functioning and us alive.  When levels of calcium and phosphorus in the blood begin to rise, Vitamin D moves them into our bones. 

Immune Health: 

Vitamin D is very actively used in our immune system.  This includes reactions to infection and the development of autoimmune diseases.  When vitamin D levels are low, we are at increased risk of more severe infection as our immune system cannot function optimally.  

Similarly, we are at increased risk of developing autoimmune conditions where our immune system confuses our tissues for infection and tries to clear them from our body while our body continues to try and repair itself.  Internal warfare against multiple body systems is not a fun way to live, as most anyone with an autoimmune condition can tell you. 

Cardiovascular Health: 

Vitamin D plays important roles in blood pressure regulation, cholesterol metabolism, and the health of the lining of our blood vessels, making it important for our cardiovascular health.  The lower our vitamin D levels, the higher our blood pressure tends to get, the more cholesterol accumulates in our blood, and the more inflamed our blood vessels get.  This is the perfect storm for heart attacks and strokes. 

Disease Prevention: 

Prevention is always better than trying to find a cure!  Over the years, there has been quite a bit of research into vitamin D and its role in disease prevention.  When you dig into the literature, there are clear associations between low vitamin D levels and certain disease processes.  What we don’t fully know at this time is whether vitamin D supplementation is effective for prevention or if natural vitamin D production is needed.  More studies are always being done to answer these questions. 

Diseases associated with low vitamin D levels: 

• Overall mortality - low vitamin D is associated with higher incidence of all causes of death. 

• Osteoporosis

• Cancer - especially colorectal and breast cancers

• Autoimmune disease - especially multiple sclerosis, rheumatoid arthritis, type 1 diabetes, and systemic lupus erythematosus 

• Hypertension

• Endothelial dysfunction - the precursor to forming plaques that can decrease blood flow to the heart and brain

• Type 2 diabetes

• Cognitive decline in Alzheimer disease

• Parkinson disease

• Acute respiratory infections - it appears that this includes COVID-19 infection and is a factor in disease severity - more research is being done and reviewed to give us a better understanding of the role of vitamin D with this new viral infection. 

Disease Treatment: 

When it comes to treating disease with vitamin D supplementation, we do see good evidence that it is useful in a few conditions, which include: 

• Atopic dermatitis - eczema

• Inflammatory bowel disease - Crohn’s disease and Ulcerative Colitis

• Hypertension

• Congestive heart failure

I suspect this list will lengthen with time. 

Where to Find Vitamin D

The majority of the vitamin D circulating through the human population is directly from sun exposure.  After this, we find vitamin D in fortified foods like milk and orange juice.  We find vitamin D naturally occurring in fatty fish and fish liver oil, and in mushrooms and yeasts that have been exposed to sunlight or artificial UVB radiation.  

Applications

So, what next you may ask?  How much sunshine should I aim for?  Should I take a supplement, and how much? 

Unfortunately, I don’t know the answer to these questions for you personally, but let’s investigate them a bit more.

Sunlight: 

We have all been made quite aware of the risk of skin cancer from excessive sun exposure.  We have also had the importance of sunscreen reinforced time and again.  I do not want to downplay these important aspects of personal care and safety, but I do wish to clarify them a bit.

Reducing the risk of skin cancer means avoiding skin damage from solar radiation - sunburns.  We want to avoid burning our skin.  How long it takes me to burn will be different from how long it takes you.  How long it takes to burn at the beginning of Summer will be different from how long it takes if you have a tan - melanin protects against UV radiation similar to sunscreen.

That being said, the higher your melanin content or the more sunscreen you use, the longer you need direct sun exposure to produce vitamin D.  Even a low SPF sunscreen can reduce vitamin D production by 90% or more! (2)  

When we try to determine how much sun is needed, one study found that those who stayed in the sun with total skin exposure just until their skin turned reversibly pink produced a level of vitamin D equivalent to taking a 10,000 to 25,000 IU vitamin D supplement! (3)  We don’t need quite that much every day, but we also do not see toxic effects from naturally formed vitamin D like we can with high dose supplements.

I do not recommend taking high levels of vitamin D daily as this can cause hypercalcemia, which can cause: 

• Kidney stones

• Bone loss

• Calcification of organs

These are all dangerous and should be avoided.  I never recommend long-term vitamin D supplementation above 2000IU daily.

Factors that decrease our ability to synthesize vitamin D: 

If you find yourself with any of the following factors that can reduce your ability to form vitamin D, you may want to consider a supplement or be strategic about eating enough foods fortified with vitamin D: 

• Lack of exposure to sunlight

• Darker skin - high melanin content   

• Genetic changes that make it hard for you to metabolize vitamin D

• Advancing age 

• Chronic kidney disease

• Liver disease

• Obesity - vitamin D precursors made in the skin can end up being stored in the subcutaneous adipose tissues and not reach the bloodstream

Vitamin D testing: 

Testing methods for assessing vitamin D levels have been improving over the years, but there is still debate about the reliability between tests as well as what form of vitamin D to test for.  Additionally, there remains controversy surrounding target levels for optimum vitamin D.  Our best available information shows us that we should be measuring 25-OH-Vitamin D levels (the form made by our liver) and that a target level should be between 30 and 100 ng/mL.  Some providers try to push for levels closer to 80 ng/mL, and there could be a case made for this in people who are at increased risk of the diseases associated with low vitamin D levels. 

Personally, I like to see measurements of vitamin D in the Fall and again in Spring at least once during a person’s life to see how they maintain levels through the relatively sunless months of late Fall through early Spring here in the Pacific Northwest.  It also shows me how much vitamin D they were able to produce over the Summer.  This helps me better make recommendations on supplementation for those seeking my care and advice.  

General supplementation recommendations: 

Here, I will defer to the Linus Pauling Institute’s recommendations.  

They recommend adults to supplement 2000IU of vitamin D3 regularly.  For children, this recommendation is 400 - 1,000IU daily.

I like to give people a vitamin D holiday during the Summer if they can and do spend at least 20 minutes outdoors without sunscreen three or more times a week. 

Next Week

Next week, we will continue our exploration of the fat-soluble vitamins with vitamin E.

To our health!

References: 

1. Higdon, J, Vitamin D, Linus Pauling Micronutrient Center, 2000, updated 2021, https://lpi.oregonstate.edu/mic/vitamins/vitamin-D accessed 6/23/2021

2. Balk SJ, Council on Environmental H, Section on D. Ultraviolet radiation: a hazard to children and adolescents. Pediatrics. 2011;127(3):e791-817.

3. Holick MF. Vitamin D: the underappreciated D-lightful hormone that is important for skeletal and cellular health. Curr Opin Endocrinol Diabetes. 2002;9:87-98.