The Sunshine Vitamin is Vital for Health, But Should You Supplement it?
I asked people at random in my office what Vitamin D was for.
Everyone had heard of it. Everyone knew it was connected with sunshine. A few had also heard it was useful in fighting viruses. One person said it was ‘something to do with bones.’ Nobody was currently supplementing.
This was a tiny sample. After a similar straw poll on simple carbs, the results were not a surprise.
I currently supplement vitamin D daily (800 IU). As with all my deep-dives, I’ll weave the clinical data with my own prior assumptions, popular myths, and longevity science. The vitamin D endocrine system does not operate in isolation – and I’ll explore closely related systems.
At the end of this guide, I’ll return to these key questions:
- Should I be supplementing vitamin D?
- If so, how much is optimal?
There are multiple forms of vitamin D. For clarity, this page covers the D3 version.
As with everything here at the Age Well Times, this is my personal deep-dive and interpretation of the clinical papers and not medical advice. Always discuss changes to your supplement routine with your doctor.
Summary: Listing the Positive Health Effects of Vitamin D
Each benefit on this list is covered in more detail (including links to the key scientific papers) below:
- Bone Health
- Reduced Susceptibility to Infection
- Skeletal Muscle Health
- Telomere Health (lowered cell senescence)
- Fat Adaption (metabolic flexibility)
After examining each benefit, the recommended doses, and risks of overdoing it are covered – before my wrap up.
Vitamin D: Bone Health was the Original Benefit
The role of vitamin D in bone heath was first described all the way back in 1953.
Vitamin D is required for the bones to take up calcium. When you are deficient, brittle bones and even rickets are possible. Clinical trials examined the link between the amount of vitamin D supplemented and bone health.
They came up blank.
The risk to bones comes from deficiency in the sunshine vitamin. Low levels are linked to osteoporosis, while boosting your levels does appear to improve bone health or susceptibility to fractures.
Calcium uptake is only one pathway that links Vitamin D to bone health. This paper links poor bone health in the elderly to the immune system, via inflammatory cytokines. Immune system regulation provided by Vitamin D helps to prevent osteoporosis by reducing inflammatory damage.
Elderly populations are more likely to be deficient in Vitamin D. And health issues which prevent older people going outside compound this.
Here are links to papers providing a broad overview the role of vitamin D in bone health:
- Meta Analysis of Trials Involving 53,537 Participants (no bone health improvement)
- Doses of Vitamin D Compared for Bone Heath Outcomes (no added benefit for 10x doses)
- Vitamin D Deficiency and Osteoporosis (deficiency a major osteoporosis risk factor)
Clinical evidence for bone health is clear.
You need a normal level of vitamin D to maintain bone health. If you have a normal level, extra supplements won’t provide extra benefits.
Infection and Immune Response Improvements with Vitamin D
Let’s set aside any debate about vitamin D and covid-19 and zoom out.
Immune system benefits are demonstrated in papers covering both response to viral infections and autoimmune conditions including Multiple Sclerosis. A major risk factor for both is a deficiency of Vitamin D. Every cell in the immune system has a receptor for vitamin D.
Deficiency risks have clear parallels with other popular supplements including Zinc and Vitamin C. Being deficient has significant health risks, while topping up from ‘optimal’ levels may not convey extra immune system benefits.
Researchers from the University of Edinburgh found a link between Vitamin D and dendritic cells. These cells act as sentinels for the immune system – calling in a response from T-cells. This paper explains more.
Vitamin D supplementation has been linked to lowered incidence of seasonal flu. A placebo-controlled study in Japan showed a statistically significant reduction in children supplementing, vs a placebo. Subsequent meta-analysis has confirmed this across age groups and doses – albeit with some caveats as to the strength of the link.
Clinical trials report a reduction in inflammatory cytokines from vitamin D . This reduction in inflammation highlights a possible mechanism for increased incidence of cancer with vitamin D deficiency. Inflammation also increases ageing through multiple pathways. This paper covers the link between vitamin D and tumorigenesis.
Short term boosts for vitamin D for patients hospitalised with respiratory infections have showed promise – but did not show statistically significant effects.
Deficiency is the key factor once again.
At chronically low levels of vitamin D, risk of viral infection and autoimmune issues skyrockets. If your levels are normal, increasing supplementation did not produce statistically significant virus-fighting benefits.
Vitamin D and Skeletal Muscle Health
Receptors in muscle cells have linked between low levels of vitamin D in the elderly and increased risk of falls.
Unlike the clear-cut papers on bones and immune health, the work on skeletal muscle shows mixed results.
One meta-analysis compared studies using functional (strength) tests. It did not find statistically significant degradation or performance improvements. Other studies have found links to the specific muscles engaged during a fall, known as fast-twitch muscles.
That old ‘more research needed’ chestnut comes up in meta-analysis documents.
There are clear results linking vitamin D levels and improvements in overall physical performance – even among Olympic athletes.
Once again, risks are on the downside – after all when you are old, a fall is more dangerous, and muscle health is lower overall. Add weaker bones to degraded muscles, and the risks of that fall turning into a fracture are increased.
Let’s watch how research into vitamin D and muscle degradation develops.
Telomere Length, Telomerase and Vitamin D
Telomeres allow for the healthy division of cells – and vitamin D has a role in keeping them long via the enzyme Telomerase.
Shortened telomeres are a trigger for cell senescence, which causes ageing via SASP (an inflammatory signalling response). Effects from vitamin D have been demonstrated in the womb. Babies born to mothers with higher vitamin D levels have longer telomeres.
This meta-analysis covers the most important telomere / vitamin D research.
This is an exciting area for longevity researchers and something I’ll be following closely.
If validated, telomere lengthening would be the icing on the cake as far as taking my regular vitamin D supplement goes.
Fat Adaption: Your Ability to Burn Fat as Fuel (for followers of the ketogenic diet)
This boost from Vitamin D comes via followers of the Ketogenic (super-low carb) diet.
It shows that Vitamin D helps use fat as an energy source – even in those not fully fat adapted. Ketosis means you are burning fat instead of carbohydrates (glucose) as your primary fuel source.
Vitamin D is stored in fat. This storage prevents us getting the benefits, especially for people with lower levels. The interesting part here is a circular relationship. As we lose fat, stored vitamin D is released – making more more available to aid burning fat. Adipose tissue is inflammatory, burning it will therefore add to the anti-inflammatory effects of vitamin D.
It is not only super-fit keto diet fans that can benefit. This study found a statistically significant link between supplementation and weight loss in obese participants.
I’m low-carb (though not keto). This area of research shows promise – though as with the other benefits, it does not highlight additional benefits above baseline levels.
Sunshine and Supplements: Get Your Vitamin D
We can make our own vitamin D – though only with the help of sunshine.
Fortunately for people in countries with dark, cloudy winters we can top up via food or supplementation. The NHS recommend everyone top up in the winter, and those with dark skin tone or are unable to get outside regularly top up all year round.
I’ll get to how much to supplement shortly, first, here is an overview on the three ways we get the sunshine vitamin:
- Sunlight: UV radiation hitting our skin reacts with 7-dehydroxycholesterol. This creates a precursor to vitamin D, which then becomes vitamin D3. The amount of vitamin D we create this way depends on sun exposure duration, skin tone, sunscreen, and the strength of sunlight (which is affected by latitude, cloud cover and time of day). Safe exposure to the sun is important – with major downsides including sunburn.
- Food: Oily fish is packed with vitamin D. Salmon, herring and (my personal favourite) sardines all boost your levels. You will also find it in egg yolks, liver and red meat including beef and pork. Vitamin D is also added to ‘fortified’ foods like breakfast cereals. For me this is like adding it to poison (refined simple carbs will cause a huge blood sugar spike).
- Supplements: Over the counter supplements are measured in ‘International Units’ or in micrograms. 10 micrograms is equal to 400 International Units. Vitamin D is fat soluble, which means it is best taken with a meal (or with olive oil). This will lead to better absorption, and the full benefit of whatever size does you take.
How Much is Too Much? The Strangely Wide Gap Between Recommended and Maximum Levels
Recommendations for how much vitamin D to take vary by country – and show a clear pattern of being revised upwards over time.
Let’s start with the UK NHS:
- 400IU (10 micrograms) between the end of September and late March each year.
- Take 200 IU (5 micrograms) of Vitamin D all year round for anyone housebound, frail, that usually cover up most skin while outdoors, or have dark skin tones.
- Do not exceed 4000 IU or 100 micrograms per day.
- There are separate recommendations for babies, young children and for pregnancy.
This page on the NHS website has more details.
Other countries have similar recommendations:
- USA: 600 IU for adults going up to 800 IU daily for over 70’s.
- Australia: 400 IU for adults with 600 IU for over 70’s.
- Canada: 600 IU for adults with 800 IU for over 70’s.
Tolerable Upper Intake Level Guidelines
The maximum regular dose of D3 recommended by these countries is a consistent 4000 IU per day. Canada provides detailed guidelines.
This is 10x the regular daily amount. There are separate clinical guidelines for people that present severe deficiency as one-off treatments. Note that this is the guideline for healthy adults.
An obvious question is whether there is any benefit to going above the recommended 400 IU per day – and importantly, any risks?
Overdosing on D3 vs. Health Benefits of Higher Doses
Take too much vitamin D over time and the result is hypercalcemia.
You need a lot of Vitamin D to get there – though the symptoms are nasty. Too much calcium in the blood causes stomach pain, nausea, weakness and may affect heart rhythm or (at high levels) cause cardiac arrest.
Impaired vitamin D metabolism, and rare genetic disorders can lead to severe hypercalcemia – which is a medical emergency.
The graphic above (adapted from this paper) demonstrates that risks from vitamin D are at the low and very high end of the spectrum. The part marked with a question mark in the middle is an area of uncertainty about additional benefits.
Government guidelines for the highest tolerable dose of the sunshine vitamin are 10x the smallest daily recommended dose at 4000 IU.
That said, clinical trials have given patients 200,000 IU for two months and then 100,000 IU for 18 months – without ill effects
Trials of single high doses during the recent pandemic showed promise, this Royal Society overview covers this topic in depth. Though were not conclusive. (LINK). A five-year trial in Finland found no benefits from high levels of vitamin D on cardiovascular or cancer outcomes.
If you are deficient in Vitamin D, then there is a case for a single high dose, followed by regular supplementation in line with age recommendations. If not, then there is no current evidence that extra D has benefits.
Wrapping Up: Low Vitamin D Levels are a Health Risk
After spending the last two days diving into the clinical papers, I’m happy that I kept up my vitamin D supplementation. 800 IU’s is a little higher than recommended. My plan is to cut back when the sunlight returns in the spring.
While I’m privileged to walk to work, and enjoy the outdoors in the summer, I’m mostly covered up. Even those delicious sardines won’t boost my levels enough to keep my telomeres long, bones strong and help fight off respiratory viruses.
It is clear to me that the single most important factor is to avoid vitamin D deficiency.
While there is clear clinical data covering bone and immune health risks for low levels, there is a striking lack of evidence for high doses having extra benefits- except as a one-off boost to people that are chronically deficient.
Some promising areas of vitamin D research include telomere health and metabolic flexibility through fat adaption.
As I finish the first draft of this guide, it is 16:30 on a damp January here in the UK – and rapidly getting dark. I’d best remember to take that vitamin D, to stay strong for the coming spring.
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