The days are getting shorter and the sun is lower in the sky every day in the Northern hemisphere. It’s time to prepare a few things for winter. One of the things that spring to mind first when it comes to potential protection from the dreaded vomiting bugs and other “nasties” that preferably make the rounds during the cold season is “Vitamin D”. We know that this hormone-like vitamin has a crucial role to play in our immune system. This is also one of the main reasons why I’m interested in the link between Vitamin D and cancer in particular.
Shift in recent years
It’s almost impossible to get away from information on Vitamin D these days. TV ads, leaflets at the doctor’s and magazine articles constantly remind us of the importance of adequate Vitamin D intake and levels. Here in Ireland, it is now “standard of care” to recommend Vitamin D3 drops to even tiny babies. This is a massive shift in recent years: When my first baby was born in 2009, I asked about Vitamin D supplements for her (given that this is one nutrient that is notoriously low in breastmilk). I was told to forget about considering ANY supplement for her. Now, the recommendation is 200 IU per day from birth. Yep, things change… and I’m grateful I had already started my studies and went ahead with supplementation anyway- the evidence was too strong at the time.
The role of Vitamin D
Vitamin D plays a role in virtually every system in the body. It’s actually better to classify it as a hormone rather than a vitamin. Its main role in the body is to maintain normal blood levels of calcium and phosphorous. But that’s not all. It has crucial effects across most body systems, especially for bones, cardiovascular, endocrine (hormonal) and immune health but also for neural and brain function. Vitamin D actually regulates the activity of over 200 genes, which a lot more than any other vitamin. And what is the link between Vitamin D and cancer? Optimum levels have been shown to reduce the risk for certain types of cancer and also the likelihood of developing autoimmune disease. In short- it certainly doesn’t do any harm having optimum levels of Vitamin D.
There’s even evidence that some chemotherapy drugs work better for certain types of cancer in conjunction with Vitamin D. Deficiency in Vitamin D is incredibly common these days- some experts even talk about a Vitamin D deficiency pandemic.
For the science nerds among you, please watch this video by Dr Holick for more in-depth information:
Sources of Vitamin D
But what exactly does this mean in practice– how can you ensure you’re protected from various diseases that are linked to a deficiency of this hormone-like vitamin? Drink more Vitamin-D-enriched milk for instance?
You’ve probably heard that “15 minutes of morning sun” is sufficient to make sure your Vitamin D levels are adequate or that all you need is “3 servings of dairy” to do the same. Unfortunately, those claims couldn’t be further from the truth.
Contrary to what a lot of people think (clever marketing?), dairy- and food in general- isn’t the best source of Vitamin D. Let’s make a comparison: A glass of milk contains about ~100IU of Vitamin D. If you have pale skin and lie outside in a bathing suit (called “modest sun exposure” in the research, meaning skin was not burned, but lightly pink 24 hours later), you’ll make anywhere from 15,000-20,000 IU of Vitamin D (Journal of Investigative Medicine, 2011). That’s quite a difference!
So, the main source of this vitamin is sun exposure and/or- if you live in Ireland, like me- supplementation. In fact, sun exposure accounts for ~90% of vitamin D in the body in individuals who do not take supplements (American Journal of Clinical Nutrition, 2004). In other words, if you’re not in the sun much or live in the Northern hemisphere, you’ll need a supplement to meet your needs. Above and below latitudes of approximately 33°, Vitamin D3 synthesis in the skin is very low or absent during most of the winter (The Journal of Clinical Endocrinology & Metabolism, 2011).
How to plan your (winter) holidays
Want to escape to a more sunny climate for a winter holiday break? Make sure you check out Ricky Sharpe’s clever graphics that depict locations across the world where the sun is more than 50° above the horizon. Basically, where UVB is able to reach the earth and we can start producing Vitamin D. Ricky plotted average times at the beginning and end of each month, then took the average for each latitude. So, depending on whether you’re travelling at the beginning or end of the month, accuracy varies a bit but you get a good starting point when planning sun holidays!
For instance, I’m travelling to South Florida in February to attend and speak at the Metabolic Therapeutics Conference in Tampa. When I look at the map for February, I can see the following:
Florida just about makes it into the 1-2 hours of “useable” sunlight a day- not great but better than in Ireland that time of the year! You can go and check out your latitude and when you can actually produce Vitamin D naturally, depending on where you live or travel to. Very useful, I think!
Other factors to consider
Interestingly, skin tone also affects Vitamin D production. I often complain about my fair skin and how difficult it is for me to tan, but I also have a significant advantage over a good friend of mine who is Brazilian and very dark skinned: I require about 3-6x less time in the sun to produce the same amount of Vitamin D as her! There’s always two sides to the coin 😉
It goes without saying/writing that if you’re putting on suncream or cover up with protective clothing, you’re not making much Vitamin D either. Sunscreen with an SPF of 30 blocks UVB rays pretty effectively, reducing Vitamin D production by 95% (The Journal of Clinical Endocrinology & Metabolism, 2011). Another useful bit of information is that the “damaging” rays that we’re always told to avoid around mid-day (between 10am and 2pm) are the ones that your skin uses to make vitamin D…
So what to do with all this conflicting advice- trying to make sure you get adequate Vitamin D without compromising skin health? There are two options: If you do go into the sun, the ideal scenario is that you get a little exposure on bare skin (without burning of course!) before using suncream or covering up with clothes. If you can do this on a regular basis during the summer months, you should be safe. The other option- say you can’t go outside at the appropriate time- you can take a Vitamin D3 supplement, which is more effective at maintaining blood levels of the vitamin than D2.
What about dosage, you may ask? The current recommended intake is set at 600 IU for adults. Note that the Institute of Medicine, IOM, increased this from 200 IU in 2010- pretty much overnight! Wow… a 3-fold increase is pretty drastic- but did they “get it right” this time? Respected researchers and doctors like Robert Heaney suggest that 7,000 IU/day from all sources is probably much more accurate.
In my experience, though, this discussion is possibly obsolete because… yes, you guess it: There is no one-size fits all dosage. It depends on your Vitamin D status and also genetic variants. And this can be tested in any hospital lab or as a convenient home test via e.g. OmegaQuant. We strongly advise that you test your Vitamin D levels twice a year and supplement accordingly under supervision of a healthcare professional.