What is Vitamin D and why do we need it?
Vitamin D is a unique vitamin!
Unlike other other vitamins, our body has the ability to generate it's own Vitamin D when our skin is exposed to sunlight; the body can't generate other vitamins, they need to be sought from the foods we eat. The other unique thing about Vitamin D is that our body converts it onto a hormone called 'activated Vitamin D' or 'Calcitriol'. Calcitriol is essential for absorbing calcium and phosphorus from your food, and for regulating the hormone that controls the amount of calcium in your blood. Without Vitamin D, these just wouldn't happen.
It has been known for many years that Vitamin D is essential for healthy bones. This was realised when children exposed to sunlight or taking cod liver oil (which contains Vitamin D) had a reduced rate of developing rickets.
But Vitamin D is not just vital for good health and healthy bones. There is much emerging evidence to suggest that Vitamin D plays a major role in preventing and treating other serious long term health problems.
What else is Vitamin D essential for?
Immune system, which helps you to fight infection
Muscle function
Cardiovascular function, for a healthy heart and circulation
Respiratory system - for healthy lungs and airways
Brain development
Anti-cancer effects
Cell production of biochemicals
Vitamin D deficiency is a term used when you don't have or generate sufficient Vitamin D. As already mentioned, Vitamin D deficiency results in rickets in children, and in adults it's called Osteomalacia. Both of these result in soft, brittle bones.
It is estimated that 40-75% of the worlds population has Vitamin D deficiency. That's more than a billion people, and people with darker skin are at higher risk.
There is growing evidence to link Vitamin D deficicency with:
Osteoporosis
Cancer (including breast, colon, lung, lymphoma and prostate)
Asthma
Type-II diabetes
High blood pressure
Depression
Alzheimer’s
Autoimmune diseases like multiple sclerosis, Crohn’s and type-I diabetes.
Pregnancy complications
How much Vitamin D do we need?
Whether you get your Vitamin D from the sun or a supplement it is sent to your liver for processing. The liver converts it into 25-hydroxivitamin D (25(OH)D), and it is the level of this substance which the GP is referring to if he tests your blood for Vitamin D.
25(OH)D is then converted by a range of tissues in the body into Calcitriol, which manages calcium levels in your blood, bones and gut, and helps cells all over your body to communicate with each other.
In order to maintain healthy levels of 25(OH)D (40-60ng/ml of blood) the body needs at least 4000 International Units (IU) of Vitamin D per day. This can either be made by exposing your skin to UVB sun rays or by eating foods or fortified foods containing Vitamin D. However, because we live a much more internal lifestyle and/or use protective sunscreen when we are outside, the average person only gets about 2000 IU/day, and that's definitely not enough.
The chart below shows the serum levels in a sample group of lifeguards who work in San Diego, California. The lifeguards were all exposed to high levels of sun on a daily basis and none took Vitamin D supplements.
The chart shows that not all of the participants had serum levels within the target range of 40-60ng/ml of blood. The average was 44ng/ml, which is at the lower end of the recommended range.
Interestingly, all the participants wore shorts and no t-shirt (as you would expect), and the average sun exposure time between 10am-2pm (when the sun is strongest) was 3.3 hours. 78% of participants used sunscreen (average SPF 30) more than half of the time, and 22% used sunscreen less than half of the time.
This shows that although sun exposure can help you achieve optimum serum levels, you have to be out in the sun for a large amount of time, and there's still no guarantee you'll produce enough, particularly if you use sunscreen.
It is recommended that the average person takes 1000-3000IU of Vitamin D per day. However, the following shows my personal Vitamin D levels, recorded approximately every 6 months (give or take!) since 2010.
I've taken 10,000IU/day of Vitamin D since 2010 to help me combat the effects of Seasonal Affective Disorder. Although some of the readings are higher than the 40-60ng/ml, this is the only way I can maintain a good level of serum, and the Institute of Medicine identify that there is no observed adverse effect with taking this amount of Vitamin D. The test where I recorded 106 was the summer I got married and I was going on a sunbed three times per week as well as taking my supplements!
My personal opinion, as well as the research evidence, is that everyone should take Vitamin D supplements because we just don't get enough sun exposure to maintain a healthy level of 25(OH)D. However, the only way to determine how much you should take is to get a Vitamin D blood test, take a supplement, get retested, adjust the amount and retest again; keep doing this until you know how the supplement affects your serum level.
Vitamin D levels are not routinely tested in the UK by your GP so it's likely that you'll have to pay for a test. In 2010 I joined a research project, first so that I could monitor my Vitamin D levels, and second, I thought if I'm getting a test anyway the results might as well be useful to the wider population.
If you want to participate in the research too you can join by going to the GrassrootsHealth website - there's a link on the home page to test your serum level. You can arrange an automatic delivery of your home testing kit every 6 months, and you need to fill in a questioannaire to get your results; it takes no more than 10 minutes to complete. Even if you don't want to have a blood test this website contains a wealth of evidence-based information.
I know I'll always take 10,000 IU/day of Vitamin D because I have 13 years worth of blood test results to tell me how much I need to take, and I also know that the cost of the supplements far outweighs the health risks of being Vitamin D deficient.........
References
Unknown (2017) Calcitiol. (online at medlineplus.gov) [Accessed 30/05/2017].
GrassrootsHealth (2017) www.grassrootshealth.net) [Accessed 30/05/2017].
Unknown (2017) What is Vitamin D. (online at www.vitamindcouncil.org) [Accessed 30/05/2017].