The importance of vitamin D and conscious sun exposure: Part 2


In the previous article, I explained why vitamin D is crucial for us, but that in the majority of the countries, over 70% of the population has vitamin D deficiency. I went through the scientific evidence that links vitamin D deficiency to many diseases, including musculoskeletal disorders, cancer, autoimmune diseases, infectious diseases, neurologic and psychiatric diseases, among others. If you haven’t read this article yet please go here.

In this second article about vitamin D, I write about:

– factors that contribute to the observed pandemic of vitamin D deficiency

– the recommended vitamin D levels

– what you can do to get there.

In my next article, I will write about the problem with sunscreens and what you can do to protect yourself from the sun naturally.


Why is there a pandemic of vitamin D deficiency?

As I mentioned in the previous article, vitamin D is produced in our skin only when we are exposed to the UVB rays. And there are certain factors that prevent us from catching enough UVBs.

  • Lack of sun exposure

We are living in a time where humans spend the majority of their time indoors. If we think from an evolutionary point of view, we (humans) have always spent a lot of time performing outdoor activities. Now, with our desk jobs, we are almost the whole day inside, so the chances of getting a bit of sun are small and we end up catching much less sun than we actually need for our health. You probably cannot change your job, but there are definitely things you can do to minimize the damage of not getting enough sun exposure. Just keep on reading…

  • Winter

As I said in my latest article, during winter and in countries in higher latitudes (e.g. Europe and North America), you will not produce vitamin D even if you are exposed to the sun, because the UVBs do not reach the Earth. If you fill up your vitamin D deposits (stored in fat cells) during summer, normally it should be enough to compensate for the lack of UVBs during winter.

But in the majority of the cases, we also do not produce enough vitamin D during summer.

  • Too much fear of catching a little bit of sun

As I said before, if you keep catching sunburns, you are indeed increasing your chances of skin cancer. But if you are not catching sun at all, you are definitely also increasing the chances of getting several types of cancers, including skin cancer, by preventing vitamin D production (please check my previous article here for more information about the link between vitamin D and cancer).

What happens is that in summer, many people cover themselves with sunscreens every time they go outside. Anything that prevents your skin from absorbing UVBs, will block your skin’s ability to synthesize vitamin D. As I said in the previous article, even a sunscreen with a solar protection factor (SPF) of only 15 already decreases the synthesis of vitamin D3 in the skin by 99% [1]. I know that health authorities have been warning us of the danger of catching too much sun and to protect ourselves by using sunscreen or clothes. This may have led to the current widespread fear of catching a little bit of sun without some kind of protection (together with the strong publicity in favor of sunscreens…but that’s another story). But what if we also start warning people of the danger of not catching enough sun? And that sun in moderation is crucial for our health?

There are also internal factors that affect UVB radiation penetration into the skin, and therefore the synthesis of vitamin D3:

  • Darker skin

Increased skin pigmentation reduces vitamin D3 synthesis, meaning that people with darker skin produce less vitamin D for the same exposure time of a whiter person [2]. African Americans with very dark skin have a SPF of 15, and, therefore, their vitamin D synthesis is reduced by 99% [2]. This might explain why the majority of African Americans who live in a temperate climate are vitamin D deficient, while Africans living near the equator, where vitamin D3 synthesis is more efficient due to the higher intensity of UVB rays, do not have vitamin D deficiency [3, 4]. And of course the same happens when we are more tanned: we need more time in the sun to be able to produce the same amount of vitamin D than when we were whiter.

  • Aging

Aging is associated with decreased concentrations of 7-dehydrocholesterol (the precursor of vitamin D3 in the skin). A 70 year old person has about 25% of the 7-dehydrocholesterol of a young adult and thus, has a 75% reduced capacity to synthesize vitamin D3 [5].

  • Obesity

Obesity is also associated with vitamin D deficiency. Vitamin D is fat soluble and is stored in the liver and fatty tissues. In obesity, there is a decreased bioavailability of vitamin D(3) from cutaneous and dietary sources, and it is thought that this is due to its deposition in the body fat tissues [6].

  • Some medications

Certain medications, including antiseizure medications and glucocorticoids (e.g. cortisone, prednisone), can also lead to vitamin D deficiency [7].


What are the recommended vitamin D levels?

A blood 25-hydroxyvitamin D (25(OH)D) level below 30 ng/ml (or 75nmol/L) is considered deficiency and levels between 30 and 100 ng/ml could provide optimal benefits for our health [8]. Indeed, a meta-analysis has shown that the mortality rate decreases until about 40 ng/ml and stays down even at higher vitamin D levels [9] (check the figure below).

Mortality rate (hazard ratio) vs serum vitamin D levels. This figure was taken from the study [9].

I think a good way to find the optimal vitamin D level is to look at populations that are still living “traditionally”, meaning in the lifestyle that humans have evolved with. A study showed that traditionally living populations in East Africa have a serum 25(OH)D concentration of 46 ng/ml (115 nmol/L) [10]. Also, population groups that spend a long time in the sun due to their job, like lifeguards and farmers, have a 25(OH)D blood level between 54 and 65 ng/ml (or 135-163 nmol/L) [11]. So, that has led to think that these are maybe the levels with which we have evolved and that we are supposed to have.

It has been shown that actual vitamin D toxicity only occurs above 25(OH)D levels of 100 ng/ml (250nmol/L), which cannot be achieved naturally (meaning, by sun exposure). They can only be achieved if you supplement continuously >10,000 IU (250 mcg) / day during several months [8]. The possible toxic effects of too much vitamin D are related to hypercalcemia, i.e. developing high levels of calcium in the blood, which can lead to some complications such as cardiac, central nervous system, renal, and gastrointestinal problems [12]. However, it has been suggested that taking high doses of vitamin D together with vitamin K2 possibly counteracts the effects of too much vitamin D. It has been hypothesized that high doses of vitamin D may deplete vitamin K storages and lead to hypercalcemia [13]. While vitamin D is needed for calcium absorption, vitamin K2 is needed to direct the absorbed calcium to the bones instead of elsewhere in the body. So, there is a close interplay between vitamin D, vitamin K2 and calcium. Without vitamin K2, calcium, absorbed due to vitamin D, might be directed to your arteries instead of your bones. Indeed, there is a lot of evidence that supports the role of vitamin K2 in the prevention of coronary calcification and cardiovascular disease [14]. In fact, supplements of vitamin K2 together with vitamin D and calcium have been shown to be useful in the treatment of osteoporosis and reducing vascular calcification [14].


Are you vitamin D deficient? What can you do about it?

I know from experience that with our desk jobs and city life, it is virtually impossible for the majority of us to reach the recommended vitamin D levels by sun exposure. However, there are things you can do to increase your vitamin D levels.

1. Check your vitamin D levels

First of all, I do recommend that you have a blood test to you check your vitamin D levels once or if possible twice per year: once in winter, once in summer (to check that you are effectively producing enough vitamin D). It is believed that the best method for determining a person’s vitamin D status is to measure the 25(OH)D concentration. So, when asking for a vitamin D test, ask for the 25- hydroxyvitamin D test.

2. Go to the sun as often as possible and be conscious with your sun exposure

As I have shown here, conscious sun exposure is vital. When we are not sufficiently exposed to the sun, we develop vitamin D deficiency, which can lead to many diseases. Now, I’m not saying that you should be in the sun the whole day and catch a sunburn. Of course this is not the goal and it is in fact dangerous. What I’m saying is that you have to be conscious about your sun exposure. A few recommendations/suggestions in order to be safely exposed to the sun:

– In the beginning of each summer and whenever possible, start exposing your skin to the sun slowly. For example, you can start with a few minutes every day (or every time you can) and increase gradually, as you feel your skin is getting more adapted to the sun.

– In order to maximize your vitamin D production, go to the sun as near to the solar noon as possible (12h-14h, when the UVB are the highest), but for a short period of time. For example, you could profit from your lunch break to go out into the sun. This will not only allow you to relax a bit, but will also provide you a natural daily dose of vitamin D.

– Now, ideally, you would be with most of your skin exposed to the sun to maximize your body production of vitamin D, for example by putting your bikini/swimming shorts on. However, I know that sometimes this is not possible, so just do your best and try to expose at least the legs, arms and belly (put your shirt up). Exposing only arms and face will not be enough. And then you can of course profit from the weekend to go to a place where you can indeed expose the majority of your skin to the sun: let’s say, the beach :). But other places would work as well of course, even your own garden/terrace/balcony.

– Concerning the time that you should be exposed, it depends on your skin pigmentation. Please start slowly with only a few minutes every day and increase gradually until about 20-30min. This should be enough to produce your daily dose of vitamin D. But his is a rough estimation, if you are very white, you will need less, if you have very dark skin, you will need more time.

– Please listen to your body! This is so important! When you feel that your skin is very warm, get out of the sun even if it’s only after 5min. You definitely don’t want to get a sunburn.

– what if you cannot or don’t want to just go to the shade? It might happen that you are outdoors during the whole day and then, you do have to get an appropriate sun protection: and by saying this I don’t mean using sunscreen. Please read my next post about the problem with sunscreens to know why I don’t recommend its use. I will also tell you safer alternatives to protect yourself from the sun, including natural sunscreens.

3. Supplementation

I do believe that we should try to get all the nutrients we need from natural sources. For example, sun exposure is important for many other things beyond vitamin D production. Namely, the blue wavelength of the sunlight is important for regulating our circadian rhythm and improve insomnia [15, 16]. It also helps to improve our mood and reduce depressive symptoms [15, 17].

However, sometimes it is really difficult to reach normal vitamin D levels due to the factors that I mentioned above. Or you might have a severe vitamin D deficiency and thus, symptoms (e.g., muscle or bone weakness) or you want to get to higher doses of vitamin D to help you recover from a disease. In these cases, I really think you should consider taking a vitamin D supplement. During winter, vitamin D supplementation might also be needed, because as I mentioned above, the UVBs don’t reach the Earth and therefore, you cannot produce vitamin D. During summer, exposing your skin to the sun in a regular basis (meaning, almost every day) should be enough to produce vitamin D. However, if you cannot be regularly exposed to the sun, you should consider taking a vitamin D supplement during summer as well.

Now, how much should you take? I recommend that you get advice from your healthcare practitioner as all of us need different levels, depending on our degree of deficiency or the vitamin D level we are aiming for. But I can tell you what research has been finding, in general.

In the absence of adequate sun exposure, at least 1,000-2,000 IU of vitamin D3 per day should be supplemented in order to achieve 30 ng/ml (or 75nmol/L) in children and adults [18, 19]. However, there are studies recommending rather 4,000 IU [20] or even 10,000 IU [8]. In fact, total-body sun exposure can provide the equivalent of 10,000 IU vitamin D/day, suggesting that this could be a physiologic limit [11].

If you are overweight or obese, your vitamin D3 supplementation should be 2 to 3 times higher [21].

If you are over 70 years old, you also have to take more vitamin D3 (at least 3500 IU) in order to reach normal levels [22].

In general, in order to enhance absorption,  vitamin D supplements should be taken with meals [23].

As probably many of you who have kids know, babies are normally given vitamin D supplements. Do you know why? Why should you give a supplement when breast milk should be the most complete food ever? Interestingly, it turns out that actually vitamin D levels in breast milk would be sufficient if the maternal vitamin D status was greater than 112 nmol/L (45 ng/mL) [24], which actually corresponds to the values in East Africans living a traditional ancestral lifestyle [10].


Thanks for reading this article :). I hope you liked it! Please check my next post about how to naturally protect yourself when you have to stay in the sun during many hours.

Live healthy 🙂




[1]          L. Y. Matsuoka, L. Ide, J. Wortsman, J. A. MacLaughlin, and M. F. Holick, “Sunscreens suppress cutaneous vitamin D3 synthesis,” J Clin Endocrinol Metab, vol. 64, no. 6, pp. 1165-8, Jun, 1987.

[2]          T. L. Clemens, J. S. Adams, S. L. Henderson, and M. F. Holick, “Increased skin pigment reduces the capacity of skin to synthesise vitamin D3,” Lancet, vol. 1, no. 8263, pp. 74-6, Jan 09, 1982.

[3]          A. R. Webb, L. Kline, and M. F. Holick, “Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin,” J Clin Endocrinol Metab, vol. 67, no. 2, pp. 373-8, Aug, 1988.

[4]          T. D. Thacher, P. R. Fischer, M. A. Strand, and J. M. Pettifor, “Nutritional rickets around the world: causes and future directions,” Ann Trop Paediatr, vol. 26, no. 1, pp. 1-16, Mar, 2006.

[5]          M. F. Holick, L. Y. Matsuoka, and J. Wortsman, “Age, vitamin D, and solar ultraviolet,” Lancet, vol. 2, no. 8671, pp. 1104-5, Nov 04, 1989.

[6]          J. Wortsman, L. Y. Matsuoka, T. C. Chen, Z. Lu, and M. F. Holick, “Decreased bioavailability of vitamin D in obesity,” Am J Clin Nutr, vol. 72, no. 3, pp. 690-3, Sep, 2000.

[7]          C. Zhou, M. Assem, J. C. Tay, P. B. Watkins, B. Blumberg, E. G. Schuetz, and K. E. Thummel, “Steroid and xenobiotic receptor and vitamin D receptor crosstalk mediates CYP24 expression and drug-induced osteomalacia,” J Clin Invest, vol. 116, no. 6, pp. 1703-12, Jun, 2006.

[8]          R. P. Heaney, “The Vitamin D requirement in health and disease,” J Steroid Biochem Mol Biol, vol. 97, no. 1-2, pp. 13-9, Oct, 2005.

[9]          C. F. Garland, J. J. Kim, S. B. Mohr, E. D. Gorham, W. B. Grant, E. L. Giovannucci, L. Baggerly, H. Hofflich, J. W. Ramsdell, K. Zeng, and R. P. Heaney, “Meta-analysis of all-cause mortality according to serum 25-hydroxyvitamin D,” Am J Public Health, vol. 104, no. 8, pp. e43-50, Aug, 2014.

[10]        M. F. Luxwolda, R. S. Kuipers, I. P. Kema, D. A. Dijck-Brouwer, and F. A. Muskiet, “Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l,” Br J Nutr, vol. 108, no. 9, pp. 1557-61, Nov 14, 2012.

[11]        R. Vieth, “Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety,” Am J Clin Nutr, vol. 69, no. 5, pp. 842-56, May, 1999.

[12]        B. Ozkan, S. Hatun, and A. Bereket, “Vitamin D intoxication,” Turk J Pediatr, vol. 54, no. 2, pp. 93-8, Mar-Apr, 2012.

[13]        C. Masterjohn, “Vitamin D toxicity redefined: vitamin K and the molecular mechanism,” Med Hypotheses, vol. 68, no. 5, pp. 1026-34, 2007.

[14]        G. K. Schwalfenberg, “Vitamins K1 and K2: The Emerging Group of Vitamins Required for Human Health,” J Nutr Metab, vol. 2017, pp. 6254836, 2017.

[15]        A. Wirz-Justice, “Seasonality in affective disorders,” Gen Comp Endocrinol, Jul 13, 2017.

[16]        J. Bass, and M. A. Lazar, “Circadian time signatures of fitness and disease,” Science, vol. 354, no. 6315, pp. 994-999, Nov 25, 2016.

[17]        G. W. Lambert, C. Reid, D. M. Kaye, G. L. Jennings, and M. D. Esler, “Effect of sunlight and season on serotonin turnover in the brain,” Lancet, vol. 360, no. 9348, pp. 1840-2, Dec 07, 2002.

[18]        M. F. Holick, and T. C. Chen, “Vitamin D deficiency: a worldwide problem with health consequences,” Am J Clin Nutr, vol. 87, no. 4, pp. 1080S-6S, Apr, 2008.

[19]        H. A. Bischoff-Ferrari, “Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes,” Adv Exp Med Biol, vol. 810, pp. 500-25, 2014.

[20]        H. A. Bischoff-Ferrari, A. Shao, B. Dawson-Hughes, J. Hathcock, E. Giovannucci, and W. C. Willett, “Benefit-risk assessment of vitamin D supplementation,” Osteoporos Int, vol. 21, no. 7, pp. 1121-32, Jul, 2010.

[21]        J. P. Ekwaru, J. D. Zwicker, M. F. Holick, E. Giovannucci, and P. J. Veugelers, “The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers,” PLoS One, vol. 9, no. 11, pp. e111265, 2014.

[22]        D. S. f. O. A. American Geriatrics Society Workgroup on Vitamin, “Recommendations abstracted from the American Geriatrics Society Consensus Statement on vitamin D for Prevention of Falls and Their Consequences,” J Am Geriatr Soc, vol. 62, no. 1, pp. 147-52, Jan, 2014.

[23]        G. B. Mulligan, and A. Licata, “Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D,” J Bone Miner Res, vol. 25, no. 4, pp. 928-30, Apr, 2010.

[24]        R. P. Heaney, “Screening for vitamin D deficiency: is the goal disease prevention or full nutrient repletion?,” Ann Intern Med, vol. 162, no. 10, pp. 739, May 19, 2015.


4 Responses to “The importance of vitamin D and conscious sun exposure: Part 2

  • Ricardo Miralles
    7 years ago

    When you said “If you fill up your vitamin D deposits (stored in fat cells) during summer, normally it should be enough to compensate for the lack of UVBs during winter”, where did you get the data from?

    I have read that the usual level of 25OH-vitamin D3 can be reduced to its half even in one day and I am in favor of the idea that this decrease is correlated with the level of aggression (including diseases) that your body suffers in that moment, since it uses the vitamin D “messenger” to activate all our best genetic knowledge to fight the aggressions.. So you will need a too big deposit for the whole winter

    • Ana Coito, PhD
      7 years ago

      Hi Ricardo. I meant in healthy people, but of course it depends on where you live. If you live for example in northern Europe you will have less periods of high UVBs than if you live in southern Europe. In a disease state, you may indeed want to increase your vitamin D levels, so I totally agree with you. If you take high doses of vitamin D, it might be important to take vitamin K2 as well, for the reasons I wrote in the article. Just to make it clear, I do think that the majority of people would benefit from taking a vitamin D supplement during winter. But I also believe that during summer, we really should profit to get our vitamin D from a natural source – the sun. Unless, as you also mention, we are so depleted and in a disease state. In that case, we would definitely benefit from a vitamin D supplement also during summer. I find interesting what you said ” level of 25OH-vitamin D3 can be reduced to its half even in one day “, do you know which scientific article showed that? It would be interesting to read in which conditions this happens. Because normally, vitamin D is stored in fat cells and its release is not immediate. That’s why there is the problem of “overdosing”, precisely because your body cannot get rid of it that fast. So I would be interested to know that source. Thank you 🙂

      • Ricardo Miralles
        7 years ago

        OK. I have not the reference with me but I did start a search to find something related.
        I found this:
        1. Reid D, Toole BJ, Knox S, et al. The relation between acute changes in the systematic inflammatory response and plasma 25-hydroxyvitamin D concentrations after elective knee arthroscopy. Am J Clin Nutr.2011;93:1006-11.
        (…”the median preoperative plasma concentration was 73 (range: 50-124) nmol/L, and this decreased by 59% by day 1 ”
        Of course this is a very aggressive situation that requires a quick defensive answer. But every disease is aggressive and a group of diseases at the same time could add their effect.
        And do not forget that by the time your levels od 25-OH vit D in serum go down, your fat pools could be empty.
        I insist: in winter time you will need to refill your vitamin D levels continuously since you can not relay on what you did accumulate in summer time (unless you were in a “very” health status.
        But I do not trust very much oral vitamin D supplements for several reasons i would recommend better to use your “natural” factory (skin) even in winter time.

        • Ana Coito, PhD
          7 years ago

          Thanks, that’s indeed an interesting finding! I do agree with you that in the majority of the situations, we would need supplementation during winter as well, as I wrote in the article.

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