July 26, 2022 9 min read

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    Vitamin D is known as the ‘sunshine vitamin’ and one many of us are found lacking, especially during the shorter, daylight hours of winter. It’s no secret that it plays many roles, from contributing to a healthy mood to fortifying immune health. 

    What remains a mystery for many people though, is  how much vitamin D is necessary for optimal health. Further, what sources of Vit D are best to get what we need all year round. In this article we examine some of the most common questions around Vit D: Can too much of the sunshine vitamin negatively affect our health? What health conditions stem from vitamin D deficiency and how much sunlight exposure do we need in order to prevent it? Keep on reading as we break out “need to know” facts about the vitamin responsible for calcium absorption, optimal mood levels, and many other functions in our body.

    What Is Vitamin D & Why Do We Need It

    We know that the sun and its rays can be harmful. Excessive  sun exposure has been linked to not only the big C, but also premature aging and skin damage. However, if there is anything that direct sunlight has been praised for (as long as you're wearing your protection!), it’s the exposure to a bioactive form of Vitamin D.  Vitamin D, also referred to as calciferol, is a vitamin that can be produced in the body endogenously when ultraviolet rays trigger its synthesis. In addition to sun exposure, vitamin D can also be obtained from both food & supplements. 

    In order to understand vitamin D better, let's briefly introduce  its two forms: D2 (also known as ergocalciferol) and D3 (also known as cholecalciferol). One of the main differences is vitamin D2 can only be found in plant sources and some fortified foods, [1] while vitamin D3 is mostly available in  animal-sourced foods and supplements. Yet, there are also high-quality  vegan vitamin D3 supplements derived from algal oil.


    It is important to note, however, that vitamin D3 is actually the vitamin D we are able to best synthesize in the body when exposed to sunlight (UV radiation). What's more, while both vitamin D2 and vitamin D3 are readily absorbed in the bloodstream,  vitamin D3 has been found to increase the overall amount of vitamin D more effectively. [1]

    But, what role does vitamin D have in our overall health that makes it irreplaceable? First and foremost, it is the support it provides to our  immune system that makes sufficient levels of vitamin D so critical. More specifically, vitamin D has a pronounced role in fighting off viruses and bacteria -  preventing infections. A study in 2017 noted that vitamin D supplementation is particularly effective in managing  the risk of acute respiratory infections. [2]

    Another prominent benefit of vitamin D relates to the health of our bones. Optimal levels of vitamin D are one of the primary precursors of long-term  bone health. Taking a vitamin D supplement consistently has been found to promote healthy bone mineralization, as vitamin D increases calcium absorption in the body. Low vitamin D levels, especially severe vitamin D deficiency, have been linked to bone pain, and even  osteomalacia - a degenerative condition that softens the bones and decreases their density, while also causing muscle weakness. [3]



    Vitamin D is also a crucial factor in  cognitive health as a calcium-regulating hormone. Low levels of the sunshine vitamin have been linked to cognitive aging, which is indicated in a study on vitamin D's role in the prevention of cognitive decline. [4]

    A study conducted by D. Guzek and colleagues also recognize the role of vitamin D supplementation in overall  mental health. [5] Taking a high-quality, natural vitamin D supplement may improve mood, help manage mood disorders, and alleviate anxiety and depressive symptoms - thus improving the overall quality of life.

    Many women also supplement with  vitamin D during pregnancy, as it has been shown to improve fetal growth, while also reducing the risk of preterm birth, preeclampsia, as well as attention disorders in children. [6] It is important to consult with a healthcare professional before introducing a vitamin D supplement (or any other dietary supplement for that matter) into your diet.


    Vitamin D Deficiency: Symptoms and Consequences

    If the health issues associated with an inadequate intake of Vit D are so widely known, how are so many people still deficient? While data from certain countries is lacking, the study concludes that approximately  1 billion people worldwide require more vitamin D. [10]

    A 2015 study recognizes  vitamin D deficiency as a global health concern - and not just in sensitive demographic groups. Unfortunately, vitamin D deficiency is a burning issue even in countries with a high level of UVB radiation, despite a diet with a substantial amount of vitamin D fortified foods. [10]

    The issue lies in the choice of vitamin D sources and the amount of vitamin D that can be obtained from them. Unfortunately, vitamin D deficiency, as well as its consequences on our health, are rather alarming in certain demographic groups. According to a study conducted by K. Y. Z. Forrest and colleagues,  vitamin D deficiency is a common health issue in the United States, especially in people of color. The study finds that approximately 42% of the population in the U.S. is deficient in vitamin D, while the percentage rises up to 82% for people of color. [7]

    Studies conducted at the Cooper Institute further confirmed that African-Americans are indeed at a greater risk of vitamin D deficiency (and all the health conditions related to it) due to higher melanin levels in  dark skin, which  limits the body's ability to produce vitamin D naturally. [8] Melanin can be perceived as a "natural sunscreen", blocking the sun exposure and preventing the UV rays from triggering vitamin D production in the body.

    While melanin is certainly the main factor in the lack of natural vitamin D production in people with a darker skin tone, it is also important to note that other aspects, such as physical activity and obesity also play a significant role in vitamin D deficiency. As with many chronic health conditions, there are always socio-economic factors at play. [8]

    Another group prone to vitamin D deficiency are  the elderly. Not only are they less likely to spend time outside, but there is also a significant decrease in 7-dehydrocholesterol levels as we age. Thinning of aging skin poses a problem for vitamin D synthesis from sunlight. [9]

    While the problem of vitamin D deficiency seems to be prevalent among the elderly, and girls and women in the Middle East, the numbers are pretty high even in adolescents, children, and infants in other regions, as well. [10]

    A lack of vitamin D in the body can manifest through frequent infections and an  impaired immune system. Since vitamin D plays a vital role in our immunity, especially when it comes to fighting off viruses and bacteria, a lack of sunshine vitamin may make us more prone to various infections, as well as colds and the flu. There is also a strong link between low vitamin D levels and respiratory tract issues, including bronchitis and pneumonia. [12]

    Not getting enough vitamin D may also affect our energy levels, resulting in tiredness, fatigue, and even low quality of sleep. Ever felt more lethargic during short winter days? Yeah, us too. Strikingly low levels of vitamin D have been linked to depressive moods and anxiety as well. [12] Feeling low during the winter months can also be caused by  seasonal affective disorder (SAD), which is often developed due to lack of sunlight and decreased production of serotonin. [14]

    Since vitamin D is one of the primary factors in  bone health, especially when it comes to the body's ability to absorb calcium, it is no surprise that inadequate vitamin D levels have been linked to chronic back pain, arthritis, and muscle weakness. Low bone mineral density due to inadequate vitamin D levels can also increase the risk of bone fractures. [12]

    An insufficient amount of vitamin D has been linked to a number of health conditions, especially if the vitamin D deficiency is prolonged. One of the main issues caused by a prolonged vitamin D deficiency in children is  rickets - a disease resulting in bone mineralization and soft bones. Even though fortified milk as a source of calcium seems to be the answer to this problem, the number of children suffering from rickets appears to be increasing globally - especially in breastfed children. [11]

    How can a vitamin D deficiency be determined? This information can be obtained from blood work, and all you need is a  25-hydroxy vitamin D test. There are also  at-home vitamin D deficiency tests that will become more and more prominent in years to come.

    Sunlight Exposure vs. Vitamin D Supplements: How To Get The Right Dose

    Vitamin-rich foods have always been important for longevity and good health. A vit D-rich diet can include fatty fish (tuna, salmon, trout), as well as cheese, egg yolks, mushrooms, and beef liver. However, the amount of vitamin D you will get from your diet depends not only on the quantity of these foods in your nutrition, but also on the diet of the animal you’re getting it from. [11]

    Though sun  exposure plays a vital role in natural vitamin D production, many factors will affect the impact of sun exposure on natural vitamin D synthesis, including skin melanin content, sunscreen, smog, length of the day, season, and the amount of time you spend in the sun.

    A general recommendation is to spend 5-30 minutes in the sun daily, between 10 AM and 4 PM, making sure to expose your face, arms, legs, and hands, without sunscreen, to promote vitamin D synthesis. [11] Another approach, according to  Andrew Huberman, is to spend 2-10 minutes in the sun as soon as you wake up, which when repeated with consistency, creates the natural wake-up signal your body needs. 

    Considering the adverse effects and risks of sun exposure, exposing bare skin without a protective layer of SPF at the peak of UV radiation isn't the healthiest way of obtaining enough vitamin D. What’s more, many people have little to no access to sunlight due to work schedules. Furthermore, if you’re living at a more northern latitude, daylight hours during winter are severely shortened. There’s simply much less sunlight to be exposed to. [11]

    When it comes to overall bioavailability, vitamin D supplements seem to be the most convenient and the most effective method of obtaining a sufficient amount of vitamin D. Since  vitamin D3 increases vitamin D blood levels more effectively than D2, and is also the main circulating form of this vitamin, it is safe to say that  vitamin D3 supplementation is a wiser choice. [1] Also, vitamin D3 supplementation is a risk-free way of obtaining the same bioactive form of vitamin D you would get from natural sunlight.

    How much vitamin D do we need?

    Blood levels of 25(OH)D less than 20 ng/ml (50 nmol/l) is considered to be an insufficient amount, while 25(OH)D less than 12 ng/ml (25 nmol/l) indicates a deficiency. Blood levels of 20 ng/ml or more are considered satisfactory, but this will also depend upon your general health and any health conditions you may be struggling with. [13]

    What about taking too much Vit D? Are there risks associated with high levels? 

    Vitamin D toxicity is a potential issue only in individuals who take extremely high doses of vitamin D over a long period of time, surpassing the  safe upper limit of 4,000 IU (international units) a day. [13]

    Healthy adults should consume anywhere between 400 and 800 IU (10-20 mcg) of vitamin D daily, while higher doses may be prescribed to people with health problems caused by a lack of vitamin D, or those at risk of vitamin D deficiency. [13]

    Certain studies have shown that  consuming 1000-4000 IU (25-100 mcg) of vitamin D daily is an extremely efficient method of promoting natural vitamin D levels and obtaining all its health benefits. However, it is necessary to consult with health professionals when it comes to increasing the daily amount of vitamin D. [13]


    You will often hear that you can get your daily vitamin D from sun exposure. This is true, but for much of the year, it’s not enough and comes with the disadvantages of sun exposure, which can be hard on your skin and promote aging. The most effective way to increase your natural vitamin D levels without compromising the health of your skin is to include a high-quality vitamin D3 supplement, which offers the same bioactive form of vitamin D as sun exposure.

    Consuming Vit-D-rich foods with healthy levels of sun exposure, and adding a daily supplement of bioavailable Vit D is the best way to ensure that you're supplying your body with enough vitamin D.


    1. Arnarson, Atli. “Vitamin D2 vs. D3: What’s the Difference?” Healthline, 2018,  www.healthline.com/nutrition/vitamin-d2-vs-d3.
    2. Martineau, Adrian R, et al. “Vitamin D Supplementation to Prevent Acute Respiratory Tract Infections: Systematic Review and Meta-Analysis of Individual Participant Data.” BMJ, 15 Feb. 2017, p. i6583, www.bmj.com/content/bmj/356/bmj.i6583.full.pdf, 10.1136/bmj.i6583.
    3. Vitamin D: Benefits, Deficiency, Sources, and Dosage.” Www.medicalnewstoday.com, 23 Feb. 2022,  www.medicalnewstoday.com/articles/161618#role-of-vitamin-d.
    4. Latimer, Caitlin S., et al. “Vitamin D Prevents Cognitive Decline and Enhances Hippocampal Synaptic Function in Aging Rats.” Proceedings of the National Academy of Sciences, vol. 111, no. 41, 14 Oct. 2014, pp. E4359–E4366, www.pnas.org/content/111/41/E4359, 10.1073/pnas.1404477111.
    5. Guzek, D., Kołota, A., Lachowicz, K., Skolmowska, D., Stachoń, M., & Głąbska, D. (2021). Association between Vitamin D Supplementation and Mental Health in Healthy Adults: A Systematic Review. Journal of clinical medicine, 10(21), 5156. https://doi.org/10.3390/jcm10215156
    6. Pérez-López, F. R., Pilz, S., & Chedraui, P. (2020). Vitamin D supplementation during pregnancy: an overview. Current opinion in obstetrics & gynecology, 32(5), 316–321. https://doi.org/10.1097/GCO.0000000000000641
    7. Forrest, K. Y., & Stuhldreher, W. L. (2011). Prevalence and correlates of vitamin D deficiency in US adults. Nutrition research (New York, N.Y.), 31(1), 48–54. https://doi.org/10.1016/j.nutres.2010.12.001
    8. African-Americans at Greatest Risk of Vitamin D Deficiency - Cooper Institute.” Www.cooperinstitute.org,  www.cooperinstitute.org/2019/09/24/african-americans-at-greatest-risk-of-vitamin-d-deficiency.
    9. HARVARD T.H. CHAN. “Vitamin D.” The Nutrition Source, 2 July 2019,  www.hsph.harvard.edu/nutritionsource/vitamin-d/.
    10. Palacios, C., & Gonzalez, L. (2014). Is vitamin D deficiency a major global public health problem?. The Journal of steroid biochemistry and molecular biology, 144 Pt A, 138–145. https://doi.org/10.1016/j.jsbmb.2013.11.003
    11. National Institutes of Health. “Vitamin D.” Nih.gov, 2017, ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.
    12. Spritzler, Franziska. “Vitamin D Deficiency: Symptoms, Treatments, Causes and More.” Healthline, 8 Sept. 2021,  www.healthline.com/nutrition/vitamin-d-deficiency-symptoms#symptoms.
    13. How Much Vitamin D Should You Take for Optimal Health?” Healthline, 4 June 2017,  www.healthline.com/nutrition/how-much-vitamin-d-to-take#What-Are-The-Optimal-Blood-Levels-of-Vitamin-D?. 
    14. NHS. “Overview - Seasonal Affective Disorder (SAD).” Nhs.uk, 12 Feb. 2021, www.nhs.uk/mental-health/conditions/seasonal-affective-disorder-sad/overview/


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