Vitamin D Action Plan
Vitamin D Action Plan

By Chris “the Kiwi” Ashenden and Liana Ashenden, PhD.


Hey mate,

I hope this finds you better than ever.

Imagine a world without the sun. There would be no warm sunshine, no green plants growing, and no vitamin D.

We may not be living in an apocalypse right now, but many people are low in vitamin D due to a lack of sun exposure. This is because our skin makes vitamin D when it is exposed to ultraviolet B rays in sunshine.


Chris the Kiwi getting plenty of vitamin D


Since the early twentieth century, scientific studies have shown that vitamin D plays a vital role in the development and maintenance of our skeletal system, throughout our lives.

In recent decades vitamin D receptors have been discovered in almost every tissue of the body, suggesting direct links with the cardiovascular, immunological, reproductive, cognitive and metabolic systems.

From an evolutionary biology point of view, vitamin D’s importance to human health is not surprising. Your ancestors, every man, woman and child of them, spent a lot of time outdoors under the sun. Sunshine is part of our evolutionary make-up.

We can get small amounts of vitamin D by eating oily fish (salmon, mackerel, herring, etc.), cod liver oil, butter oil, and eggs. Many people now take vitamin D supplements.

But by far the best way to obtain vitamin D is through sun exposure. I am going to say this again and again.

Yes, I want you to get out in the sun.


Photo by Christopher Bertram. Oily fish like these herring provide a dietary source of vitamin D, a good start, but the SUN is a lot better.


In today’s world a lot of people don’t regularly expose their bodies to the sun. There are many reasons for this: cultural (wearing clothing in public), practical (working in an office), habitual (relaxing with TV), learned (using sunscreen, which blocks UVB rays), and seasonal (staying indoors when it’s cold).

It’s winter in the northern hemisphere right now. If you’re living more than 35 or 40 degrees above the equator, you’re coming to the end of what’s known as the ‘vitamin D winter’, and chances are you’re vitamin D deficient. Check a map, folks – that includes the USA north of the sunshine states, Canada, the UK, Scandinavia, most of Europe and Eastern Europe, Russia, parts of the Middle East and half of China.


Image by David Monniaux, modified by Liana Ashenden. The northern hemisphere ‘vitamin D winter’.



When was the last time you felt the sun on your bare skin?

Let’s be clear – I’m not suggesting you take risks in the sun. Too much UVB radiation can lead to cataracts, skin damage, and basal cell and squamous cell carcinoma skin cancer. But no exposure to UVB can lead to other health problems. Don’t avoid the sun, just be smart about it.

I strongly recommend that you read the post I wrote last summer on how to ditch the sunscreen and still get sunshine on your skin SAFELY and INTELLIGENTLY. I’ll also give a short summary at the end of this post.

Today, I want to explain more about vitamin D and help you to figure out whether you’ve got enough of it. Your Vitamin D levels depend on a whole host of factors.


What is vitamin D and how does it work?

Vitamin D is called a ‘vitamin’ for historical reasons, but it’s really a pro-hormone (a substance that can be converted into a hormone). Unlike the other vitamins necessary for growth and health, we don’t need a dietary source of vitamin D, because our bodies can make it through direct sun exposure.

The type we make in our skin and eat in our diet is vitamin D3, or cholecalciferol. It’s a fat-soluble steroid and biologically inert in this form.

In the liver cholecalciferol is converted to calcidiol, the body’s main storage form of vitamin D. Calcidiol is a pre-hormone (a secreted hormone precursor) and low levels of it in the blood give a good indication of vitamin D deficiency. If you have a blood test, this is what they will measure.

Enzymes in the kidneys and other tissues convert the storage form, calcidiol, into the biologically active hormone, calcitriol. Calcitriol is a potent steroid hormone with many biological actions. Its half-life is about two weeks in the blood and two months in fat tissue.

The active form of vitamin D mediates its effects through a vitamin D receptor in the cell nucleus. When calcitriol binds to the receptor, it regulates the expression of certain genes. The nuclear vitamin D receptor is expressed in most tissues and cells in the body (in fact, cells without it are the exception rather than the rule) and scientists estimate that calcitriol or the lack of it can affect the expression of hundreds of different genes.


Image by Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute Deutsch. Diagram of the vitamin D receptor found in cells throughout our bodies


Vitamin D is now regarded as an important signalling molecule. It has both direct and indirect biological effects in the body on mineral homeostasis, bone mineral density, cell differentiation and proliferation, cell death (apoptosis), hormone production, and the immune response.


Short version:

  • Nearly every cell and tissue in your body has vitamin D receptors.
  • Want your bones nice and strong? Get enough vitamin D.
  • Want a healthy immune system? Get enough vitamin D. 


What are the health benefits of Vitamin D?

Healthy bones

The best known and researched effects of vitamin D are on the health of your skeletal system.

Vitamin D was first discovered 90 years through the study of rickets, a disorder in babies and children characterised by weakening and deformity of the bones. Both rickets and its adult form osteomalacia are caused by a lack of vitamin D, calcium, or phosphate.


Photo by By Mrich at en.wikipedia. 5 X-ray showing leg bone deformities in a child with rickets


Vitamin D deficiency is also linked to osteoporosis. Randomised clinical trials show that vitamin D supplementation increases bone mineral density and reduces the risk of falls and fractures in the elderly. The effects of these trials depend on baseline calcium intake, baseline vitamin D status (supplementation is more effective in people who have vitamin D deficiency to begin with), age, residence and gender (post-menopausal women appear to benefit more).

Calcitriol plays a key role in calcium and phosphate homeostasis. Without vitamin D, cells in the small intestine would absorb only 10-15% to 15% of dietary calcium and 60% of phosphorus for transport into the circulation. In the kidneys, calcitriol stimulates the re-absorption of calcium from the glomerular filtrate. Calcitriol stimulates the maturation of bone cells.

A low calcium intake heightens the effects of vitamin D deficiency; a high calcium intake increases the serum half-life of vitamin D (but may have other health consequences, such as kidney stones and, potentially, increased cardiovascular risk).

Putting it another way, vitamin D can be considered a set of traffic lights that directs your body to use calcium efficiently for bone mineralization. Without sufficient vitamin D, it is a waste of time (and potentially dangerous) just adding more and more calcium to the mix. Go tell your Doctor.

High quality randomized controlled studies of the effect of vitamin D on skeletal health are lacking in babies, children, pregnant and breastfeeding women, premenopausal women, and different racial and ethnic groups.


Non-bone health outcomes

The vitamin D receptor is expressed in cells in almost every tissue of the body. This widespread distribution and vitamin D’s function as a signalling molecule and hormone strongly suggest that it plays an important role in the body as a whole, not only in skeletal health.

The active form of vitamin D, calcitriol, has stimulatory and inhibitory effects on cell proliferation and differentiation, the production of insulin, renin, parathyroid hormone, oestrogen, and testosterone, and the immune response.


That means pay special attention if you care about your:

  • Sex hormones
  • Blood sugar regulation and insulin resistance
  • Thyroid function and health
  • Blood pressure
  • Immunity from disease


It also prompts its own destruction by up-regulating the expression of enzymes that convert calcidiol and calcitriol into inactive forms.

Observational and longitudinal cohort studies show correlations between low vitamin D levels and conditions such as cardiovascular disease, breast, prostate, and colon cancer, stroke, obesity, infection, metabolic disorders (including inflammation and diabetes), autoimmune disorders, and cognitive disorders.

However, the evidence from these studies is inconsistent and inconclusive at this stage. Correlation does not equal causation, something I really, really wish the Media, your local MD, and Dr Oz would stop and think about, but I digress.

As yet there is limited direct scientific evidence that having low blood serum levels of vitamin D leads to these conditions, or that having sufficient vitamin D levels protects against them.

Large, well designed, randomized controlled trials are needed, as well as studies that scrutinise the role of confounding factors.

The scientific literature may not yet provide the full story of vitamin D’s role in non-bone health outcomes, but optimising our levels of vitamin D seems very, very sensible based on the evidence so far.

I do NOT think it is an accident that incidence of colds, the flu, and of upper respiratory tract infections are VASTLY lower in summer than in winter, for starters.

Which of course, just begs the next question…


What is the optimum level of vitamin D?

Vitamin D levels are determined by measuring the blood serum concentration of calcidiol, or 25(OH)D. The optimum level of vitamin D for health is controversial, but it would appear that approximately 35ng/ml provides peak bone mineral density and protects against fractures and falls.

The Endocrine Society and Institute of Medicine define critical vitamin D deficiency as < 20ng/ml. The main cause of deficiency is inadequate exposure of the skin to sunlight, and it is very common.

Is it possible to have too much vitamin D? Yes, although toxicity from hypervitaminosis D is very rare, and people are far more likely to be at risk from vitamin D deficiency.

Sun exposure doesn’t lead to overdose because the body has its own defence mechanisms – burning and the pigment melanin prevent the skin from producing excessive vitamin D.

Dietary sources and supplements in sensible doses are also safe. You are only at risk of overdosing on vitamin D if you take crazy mega-doses of vitamin D supplements (40,000-100,000 IU per day for several months), causing an influx of calcium. Symptoms of hypercalcemia in the blood include poor appetite, nausea, vomiting, constipation, weakness, frequent urination, thirst, dizziness or confusion, and kidney damage. It is treated by stopping vitamin D supplements and restricting calcium intake, and in severe cases corticosteroids or bisphosphonates are prescribed to reduce calcium levels in the blood. Since vitamin D is stored in fat tissue, the effects of toxicity may last for months despite stopping external sources of vitamin D.

It should also be added that if you are obese, you may need more Vitamin D, since your fat tissue will store it (steal it?).


What is your vitamin D profile?

Your vitamin D levels depend on your environment, sun exposure, diet, and who you are:

  • Season, latitude, altitude, weather, time of day, atmospheric filters, and reflective surfaces determine how much UVB is in the sunlight around you.
  • Time in the sun, amount of clothing, and sunscreen affect your skin’s exposure to UVB and therefore your vitamin D production.
  • Diet and supplements affect your vitamin D levels and effectiveness.
  • Your skin colour, age, reproductive status, and health have an impact on your vitamin D levels.


Look at the following chart. Which my wonderful sister Liana was so nice to draw and build out.

How many of the factors associated with low vitamin D production apply to you?

What is your personal profile?

The more items down the left that apply to you, the more likely you are to be at risk for vitamin D deficiency.




Variable Description
  • The Earth’s atmosphere filters out UVB. When the sun is low in the sky, sunlight passes through more of the atmosphere before it reaches you. As a result, your skin receives less UVB and you make less vitamin D3.
  • Time of day. Exposing your skin in the middle half of the day (i.e. close to solar noon) produces more vitamin D3 (but pale skins are more at risk of burning at this time).
  • Season. There is less UVB in sunlight in winter.
  • Latitude. The further away from the equator you are, the longer the ‘vitamin D winter’ lasts, and the less vitamin D you can produce.  People living in the band of tropics within 35 degrees north or south of the equator can produce vitamin D all year.
  • Altitude. People living at high altitude have less atmosphere above them and are exposed to more UVB than people living at sea level.


UVB filters
  • The following filter out UVB and reduce your ability to produce vitamin D: heavy clouds, ozone, air pollution, glass windows, sunscreen, and clothing.


Reflective surfaces
  • Surfaces that reflect the sun’s rays can increase your overall UV exposure. Fresh snow reflects up to 80% of UV radiation, sea foam reflects 25%, dry beach sand reflects 15%, and grass, soil and water reflect less than 10%.


Skin exposure
  • Exposing your whole body to the sun massively increases vitamin D production. The torso is more effective than the hands and face.
  • How much time you spend outdoors, and in the sun or shade, impacts on UVB exposure.
  • Do you cover up with clothing or headgear when outside? Do you wear sunscreen or cosmetics containing sunscreen? Factor 30 reduces your skin’s vitamin D synthesis by more than 95%.


Diet / supplements
  • Dietary sources of vitamin D include salmon, mackerel, herring, cod liver oil, butter oil, eggs, and artificially fortified foods.
  • Fat consumption is important, since vitamin D is fat-soluble and made from cholesterol.
  • Vitamin D3 supplements can be derived from lanolin, cod liver oil extract, or synthesised from 7-dehydrocholesterol.
  • Vitamin D2 supplements can be derived from UV irradiation of the yeast sterol ergosterol or from sun exposed mushrooms.
  • Levels of vitamin A, vitamin K, calcium and phosphorus affect the effectiveness of vitamin D in the body.


Skin colour
  • The skin’s pigment, melanin, is the body’s natural protection against DNA damage and vitamin D toxicity from too much sun exposure.
  • If you have pale skin, you make vitamin D quickly when your skin is exposed to the sun, but you are more at risk of sunburn.
  • If you have dark skin, it may take 3-6 times longer for you to make vitamin D, and you may be vitamin D deficient.


  • Babies, children, and elderly people produce less vitamin D.
  • You produce more vitamin D between the ages of 20 and 60.


Health conditions / medication
  • People with the following health conditions may be vitamin D deficient and need MORE: obesity, fat malabsorption syndromes, thyroid disorders, chronic inflammation, Crohn’s disease, coeliac disease, diabetes, and some types of liver and kidney disease.
  • People who have recently spent a long period in hospital may be vitamin D deficient due to a lack of sun exposure.
  • People taking the following medications may be at risk of vitamin D deficiency: anticonvulsants, barbiturates, antacids, replacement hormones, corticosteroids, anticoagulants, blood thinners, and some anti-HIV medications.



Kiwi, what should I do?


Photo by Liana Ashenden. In summer time, your skin rapidly produces a large amount of vitamin D when you expose your whole body to the sun for 10-60 minutes (the length of time needed depends on your skin colour, latitude, and time of day).


By now you should have a rough idea of your own vitamin D profile using the images and chart above. For example, if you have dark skin and you’re living far north of the equator, chances are you’re deficient.

If you are obese, have GI problems such as leaky gut which will effect your ability to absorb dietary Vitamin D, or any thyroid or auto-immune issue, it is likely you need more vitamin D.

Eat oily fish and eggs, which contain vitamin D3.

Consider supplementation with a quality source of vitamin D3, such as cod liver oil if you can palate it or Athletic Greens’ Vitamin D3.

It goes without saying, but I’ll say it anyway: if you are on medication seek your doctor’s medical opinion before taking any supplement.

How much should I take? Many studies show a u-shaped dose response curve with vitamin D supplementation. This means that, in some situations, very high doses of vitamin D may actually have the opposite (negative) effect of low doses. A meta-regression of trials published over a 25 year period showed that, in the absence of calcium co-supplementation, the average increase in serum calcidiol concentrations was 0.78 ng/ml per mcg of vitamin D supplement per day. 1mcg of vitamin D supplement is equivalent to 40 IU.

Get blood tests to check your progress if you are not getting the bulk of your vitamin D from direct sun exposure.


I ABSOLUTELY recommend the sun. For all of you who are not getting at least 5 days a week of a MINIMUM of 10-30 minutes of direct sun exposure, then I recommend doses of 1000-5000 IU daily, but only on the days that you are not out in direct sun.


  • 5 days a week or more of direct sun – you don’t need any supplementation (consider getting levels checked if you get sick a lot or feel less than perky, or have three or more of the left hand columns apply to you from the above chart, as you may not be getting enough sun).
  • 3 – 4 days a week of 10-30 minutes plus of direct sun – unless you are in the equator or enjoying long exposure on your sun days, take 1000-2000 IU of vitamin D3 on the days you are not in the sun, or 4000-5000IU every second day.
  • 1 – 2 days a week of sun, or less – take 3000-5000 IU of Vitamin D3 on the days that you are not in the sun.
  • Blood tests – If you are in the last low/no sun camp, then at 4 and 12 weeks of supplementation, I recommend you go and get your vitamin D measured, which is a simple blood test. If you are below 35ng/ml, keep on doing what you are doing and retest at 12 weeks. Consider that you need both a healthy gut and adequate fat and cholesterol in your diet to absorb and make vitamin D3. Again retest at 12 weeks. If you are above 50ng/ml, stop vitamin D supplementation altogether. If you are between 35 and 50ng/ml, then to my mind, you are on the money. If you are of Northern European extraction with pale skin, then some evidence suggests that the lower end, 20-35ng/ml, may be ideal. If you are of equatorial extraction with darker skin, then aim for the higher level


Either way, if you are even remotely low: GET MORE SUN.

Please note, that if you have any type of GI issue, you are at risk of having very poor absorption of your Vitamin D3 and will need a higher intake.


You are under no obligation, but you can check out our Vitamin D3 product here —> Athletic Greens Vitamin D3.  If you are already an Athletic Greens Loyalty customer, just email support (at) and they can instantly add Vitamin D3 to your next shipment at the lowest possible cost.


Note: Some of you may have seen vitamin D2 in shops. This type is not found naturally in the human body and is less effective at raising serum calcidiol concentrations. It is derived from UV radiation of yeast and certain mushrooms. I recommend you skip the Vitamin D2.


By far the BEST way to rebuild your vitamin D levels is by exposing your skin to the sun in a safe way. Check out my previous post.

In the winter far away from the equator, try to expose your skin as much as possible to sunlight at solar noon each day. Get out of the office at lunch time, go for walks in the sun. Your risk of sun damage is low at this time of year. Remember that snow reflects the sun’s rays and can increase UVB levels.

In the summer, and especially if your skin is pale, build up gradually with short amounts of time in the sun. Listen to your body’s natural alarm system and don’t allow yourself or your children to get burned. Move into the shade, stay out of the midday sun (10am-2pm), and cover up with sunhats and clothing rather than sunscreen. Protect your eyes with sunglasses that block out UV rays.

People with fair, freckly skin and red hair need to take extreme care in summer sun. Limit your exposure to a few minutes early or late in the day and cover up at other times. You produce a different kind of melanin, called pheomelanin, which is less effective than eumelanin at protecting your skin from UV damage and may increase your risk of skin cancer.

If you have fair skin and expose your whole body to summer sunshine without clothing or sunscreen, you can make 10,000-20,000 IU of vitamin D in 10-30 minutes. If you have dark skin and do the same, you will need to spend many times longer in the sun to make the same amount of vitamin D.

The sun, treated with respect, is the best way to improve your vitamin D levels. It’s also a great way to increase happiness.

Go get your sun mate. You will thank me for it.


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About the author
Chris 'The Kiwi'
So named because he comes from a little country in the Pacific called New Zealand where a small, fat, quasi-blind, and largely defenseless bird by the name of “Kiwi” is the national animal, and what we are called when we land in other countries. He is focused on using what he can remember from his studies for a BSc in Sport and Exercise Science and his cumulative years as a nutritionist and strength coach to help other people enjoy amazing levels of health and energy. He enjoys ticking through his list of life goals and meeting new people.
  • drtg


  • nzredhead

    Heya. I moved to Michigan a couple of years ago from NZ to join a D1 sports team at Michigan State while studying a major dietetics. Going from the food back home to here is a huge change I reckon and I have since started following a pretty strict vegetarian diet. I am pretty focused on my sport and don’t want anything I do in my diet to impact my performance in a negative way (obviously!). I have only briefly read a few of your articles, but am quite interested why you say to avoid nuts and seeds?? Would you please be able to explain this for me or direct me to an article? Cheers!

  • Nick

    Hi Chris, I am in the USA and have tried your AG for 3 weeks. I have been experiencing acid reflux problem for two years and wondering if taking AG will help it.

    • Anonymous

      Hey Nick,

      Athletic Greens will, but even more so will an intelligent eating plan.
      Read the links and follow that advice and you will do just fine mate.

      Chris Ashenden

  • Anonymous

    Hey Sam,

    Thanks for your message, sorry to hear about your son.

    YES, get him the heck off Dairy.

    Also get him off ALL

    and for a while, no nightshades, nuts, or seeds

    he can reintroduce the last once he is up and running again and puts both into remission.

    glad you caught it early!


  • acustomer

    You might want to take a look at some studies that are gaining traction that say vitamin K2 is required to successfully use both calcium and Vitamin D to ensure that calcium is absorbed by bone instead of arterial wall etc. Some studies contraindicate calcium and Vitamin D unless there is sufficient Vitamin K2.

    • Anonymous

      Hey mate. The Vitamin K post just went up. Also, I typically assume that all my readers are eating off a pretty close to paleo template AND taking Athletic Greens, in which case they are covered for K1 and K2. Appreciate the comment

  • Anonymous

    Thanks for this great and super in-depth article.

    I do disagree with a few things though:

    1. The range of 35-50ng/ml is far too low. This is a bit speculative but I’d estimate an ideal blood range is more in the 70-100 ng/ml.

    2. Vitamin K2. You need to supplement that if you take Vitamin D.

    • Anonymous

      Hey mate. Thanks for the comment. I used to be in the higher is better range as well, but some recent studies have come out suggesting that that is not the case. The human range in this is quite astounding. In terms of K, I love vitamin k2, and just posted on this. Cheers, C

      • Anonymous

        Chris, thanks for your response. Just skimmed the Vitamin K post and it looks awesome. Can’t wait to read it in detail.

        Do you have the references for the studies suggesting lower blood levels might be better? I only saw one with Scandinavians thought it looked a bit questionable. Would love to see the studies you mention though.

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