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Have you ever wondered why doctors, nutritionists, and those in your life keep talking about vitamin D? There's a good reason. This powerhouse nutrient does way more than just help your body make energy — it's crucial for everything from keeping your bones strong to boosting your mood. But here's the caveat: even though we can get it from sunshine, many of us still aren't getting enough. Let's dig into why this vitamin is such a big deal, where to find it, and how to make sure you're getting what you need.
Key Takeaways
- Vitamin D supports overall health, helping with everything from bones and your immune system to mood and energy levels.
- Not getting enough vitamin D can make you feel tired, weak, and more prone to getting sick. It can also affect your bone strength and mental well-being.
- Most people get vitamin D from sunlight, but factors like the daily use of SPF, skin color, age, and where you live can make it difficult to get enough naturally.
- Most adults need about 600 IU of vitamin D daily, but too much can actually be harmful, so it's best to talk to a doctor about the right amount for you.
- Vitamin D is critical in regulating immune responses, supporting the body's defense mechanisms, and potentially reducing the risk of various chronic health conditions.
What Is Vitamin D?
Also called calciferol, vitamin D is a well-known fat-soluble nutrient involved in maintaining healthy bone mineral density. Its two main forms are cholecalciferol (also known as vitamin D3) and ergocalciferol (aka vitamin D2). It regulates calcium and phosphate metabolism by acting on the small intestine, kidneys, and bone.1
When vitamin D is ingested through diet or synthesized in the skin from sunlight, it’s converted into active forms in the liver and kidneys, respectively. It promotes calcium absorption in the gut and supports adequate serum calcium and phosphate concentration to allow normal bone mineralization and prevent low serum calcium from leading to tetany (involuntary contraction of muscles causing cramps and spasms).
Why Is Vitamin D Important?
Like vitamin B3 deficiency, which affects cellular nutrition and energy production, vitamin D deficiency can impact multiple body systems. Vitamin D has a uniquely broad impact on human health. While its classic role in bone health is well-known, research has revealed that vitamin D benefits extend throughout nearly every system in the body.
Acting more like a hormone than a typical vitamin, vitamin D influences thousands of genes and helps regulate numerous cellular functions. While most nutrients come primarily from our diet, vitamin D follows a different path. Our bodies mainly produce it when sunlight hits our skin, with food sources and vitamin D supplements serving as important secondary sources.
This unique characteristic, combined with our modern indoor lifestyle, helps explain why maintaining healthy vitamin D levels has become such a crucial health consideration. So, why is vitamin D important? Let’s take a look at a few essential vitamin D benefits:
Vitamin D and Immune System Support
Vitamin D is also a hormone that helps regulate the immune system. Studies show vitamin D plays an important role in both the innate and adaptive immune systems.
Suggestions linking vitamin D and immune function in part originate from observations of disease occurrence based on geographic location. Vitamin D is primarily obtained through synthesis in the skin following sun exposure, and levels of UV light vary according to latitude (distance from the equator). Higher latitude is often an indicator of lower levels of UV exposure and lower vitamin D status. The incidence or prevalence of a disease increases with increasing distance from the equator.
Innate and Adaptive Immune Systems
Research has shown vitamin D is involved in the innate and adaptive immune systems. Several cell types of the immune system, including T cells, B cells, neutrophils, and macrophages, express the Vitamin D Receptor (VDR), symbolic of their capacity to be decreased by vitamin D signaling. Vitamin D is involved in the antimicrobial activities of macrophages and monocytes2,4 and antiviral activity against many respiratory viruses5,6.
Vitamin D and its metabolites exert multiple phenotypic effects on the vascular endothelium via multiple pathways that are protective against vascular dysfunction and tissue injury1. Furthermore, multiple studies have shown that vitamin D plays a role in gut integrity and intestinal homeostasis between host and gut microbiota. Signaling vitamin D increases the viability of intestinal cells and eases intestinal damage from bacteria that activate the immune system.
Vitamin D’s role in the innate immune system has important clinical implications, made evident by the increase in vitamin D-deficient individuals, resulting in thean increased susceptibility to bacterial infection1.
Adaptive Immunity
While vitamin D enhances the innate immune system, it suppresses adaptive immunity by suppressing the response of type 1 helper (Th1) cells that are capable of producing inflammatory cytokines.3
Vitamin D’s role in the adaptive immune system can have consequences for the occurrence of autoimmune diseases with uncontrolled adaptive immune activation. Geographically, the incidence of multiple sclerosis (MS) or inflammatory bowel disease (IBD) is less prevalent for those who live closer to the equator, potentially due to the ability to make vitamin D from UV light, the most favorable source. Vitamin D deficiency is associated with an increased incidence of MS and IBD.3 Research indicates the importance of active vitamin D (1,25(OH)2 D3) as a regulator of primary components of the immune system.
Vitamin D and Bone Health
We often think of vitamin D as beneficial to bone health. Vitamin D is crucial to calcium and phosphorus homeostasis and subsequent bone metabolism. Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate levels to enable normal bone mineralization. Normal bone mineralization is a result of highly specialized cells. Bone growth occurs via bone-building cells called osteoblasts. Bone remodeling occurs through osteoclasts—cells that break down bone. These cells work synergistically with one another to constantly remodel bone.
Along with calcium, vitamin D helps to protect against osteoporosis, or brittle bones. Women are at substantial risk for osteoporosis and subsequent bone fracture when they are post-menopause because estrogen levels decline significantly during this time, causing a decline in bone density. Estrogen protects bone integrity.
As an aside, some younger women can also be at risk for bone loss and fracture, including those who fail to menstruate due to an eating disorder and excessive weight loss. These women also have limited estrogen exposure as a risk factor. Vitamin D may help to reduce the risk of fractures.
Vitamin D and Mental Health
Scientists have discovered vitamin D receptors throughout the brain, particularly in areas that regulate mood and behavior.
When you're low on vitamin D, it can affect your brain's production of serotonin, often called the "feel-good" chemical. This explains why people often experience mood changes during darker winter months. Studies show that maintaining healthy vitamin D levels may help reduce symptoms of depression and anxiety, though it's just one piece of the mental health puzzle.7
While vitamin D supplements can help, they work best as part of a comprehensive approach to mental wellness that includes other lifestyle factors.
Vitamin D and Cardiovascular Health
Research has revealed significant connections between vitamin D and cardiovascular function. While initial observational studies suggested that higher vitamin D levels might directly improve heart health, recent clinical trials have provided a more nuanced understanding. Vitamin D plays several key roles in cardiovascular health. It helps regulate blood pressure, reduces vascular inflammation, and supports the health of cells lining the blood vessels.8 When vitamin D deficiency occurs, it can lead to various cardiovascular risk factors.
However, newer research has shown that high-dose vitamin D supplements don't necessarily provide additional cardiovascular benefits beyond those achieved with moderate intake. Vitamin D helps maintain proper cardiovascular function, but these benefits appear to plateau once sufficient levels are reached. Studies indicate that maintaining adequate vitamin D levels through reasonable daily intake is just as beneficial as taking high-dose supplements.9
Vitamin D and Brain Health
The brain contains numerous vitamin D receptors in regions responsible for cognition, mood regulation, and memory formation. Vitamin D deficiency may cause neurological and psychological conditions. Studies indicate that maintaining adequate vitamin D levels supports essential brain processes, including neurotransmitter production, nerve growth, and protection against oxidative stress.
Research has shown particularly strong connections between vitamin D deficiency and cognitive decline, especially in older adults. Clinical studies have found correlations between low vitamin D levels and increased risk of dementia, while proper vitamin D supplementation may help maintain cognitive function.10 The aging process can affect how efficiently our bodies process vitamin D, making monitoring levels increasingly important as we age.
Vitamin D and Nervous System Health
There are vitamin D receptors throughout the nervous system, and this nutrient helps to protect and maintain nerve tissue. Research shows that vitamin D helps regulate the production of important neurotrophic factors — proteins that support nerve cell survival and function — while also helping maintain calcium homeostasis in nerve cells.11,12
Clinical studies found that vitamin D deficiency can potentially increase the risk of central nervous system (CNS) disorders, including multiple sclerosis. The research suggests that adequate vitamin D intake, particularly during pregnancy and early development, may be important for preventing these conditions.13
What Are Symptoms of Vitamin D Deficiency?
Vitamin D deficiency often develops slowly, which means the symptoms can be easily missed at first. While many people might not notice any immediate signs, vitamin D deficiency can affect multiple systems in your body over time. How your body makes energy and maintains various functions can be significantly impacted when vitamin D levels drop too low.14
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Fatigue and low energy: One of the first signs of vitamin D deficiency is often unexplained tiredness and a general lack of energy. This happens because vitamin D supports cellular energy production and muscle function.
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Bone and joint pain: Since vitamin D helps your body absorb calcium, low levels can lead to bone pain and discomfort in your joints. This may be noticeable in your back, hips, and legs, where the pain might range from a dull ache to more severe discomfort.
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Muscle weakness: Along with fatigue, you might notice muscle weakness, particularly in your arms and legs. This can affect your balance and make climbing stairs or getting up from a sitting position more difficult.
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Weak immune system: Adequate vitamin D levels are essential for maintaining a strong immune response. When you're experiencing vitamin D deficiency, you might get sick more often or take longer to recover from illnesses.
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Hair loss: Vitamin D helps create new hair follicles, and low levels might affect normal hair growth cycles.
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Delayed wound healing: Your body needs vitamin D to create new skin cells during the healing process. When levels are low, cuts, scrapes, and other wounds might take longer to heal.
Who is at Risk of Vitamin D Deficiency?
In the past, severe vitamin D deficiency presented as rickets, which is now a rare bone disease in children. Those who lack adequate sun exposure, have conditions of malabsorption, or diets poor in fortified foods are at risk for low vitamin D. Vitamin D deficiency can be diagnosed with a simple blood test, and supplementation can be suggested based on results.
Older adults are at increased risk of developing vitamin D insufficiency, partly because the skin’s ability to synthesize vitamin D declines with age. In addition, older adults are likely to spend more time than younger people indoors, and they might have inadequate dietary intake.
People with darker skin are also at higher risk of vitamin D deficiency because melanin pigment, while protecting against UV damage, also reduces vitamin D synthesis. Research has shown that individuals with more melanin need more sun exposure. In areas with limited sunlight, this can put people with darker skin at greater risk of deficiency than their lighter-skinned counterparts.15
Sources of Vitamin D
The primary source of vitamin D is through synthesis in the skin from sunlight and ultraviolet (UV) light exposure.
Synthesis is dependent on multiple factors. Season, time of day, length of day and light exposure, cloud cover, smog, skin melanin content, and sunscreen can all affect UV light exposure and vitamin D synthesis. Older people and people with dark skin are less able to produce vitamin D from sunlight and are thus more at risk for deficiency. It’s also worth noting that UV light is not absorbed through glass.
Vitamin D in Food
Vitamin D is difficult to find in food. Vitamin D3 is found in fatty fish such as trout, salmon, tuna, and fish liver oils. Smaller amounts are found in beef liver, cheese, and egg yolks. Mushrooms provide varying amounts of vitamin D2 naturally. Some mushrooms have been treated with UV light to enhance the level of vitamin D2. Foods that have been fortified with vitamin D provide the majority of dietary vitamin D in America. Fortified foods include dairy milk and yogurt, infant formula, orange juice, and breakfast cereal.
Vitamin D Supplementation
Vitamin D supplements contain vitamin D2 or D3. Vitamin D2 is the plant-based source of vitamin D and is produced using UV irradiation of ergosterol in yeast. Vitamin D3 is manufactured through irradiation of 7-dehydrocholesterol from lanolin found in sheep’s wool. Lichen offers an animal-free source of vitamin D3.4
The vegan vitamin D3 found in Tru Niagen Immune is derived from algae. Our NAD+ supplements provide a targeted approach to supporting cellular health by replenishing NAD+, a critical coenzyme that naturally declines with age. Since NAD+ levels decline with age, a supplement can help maintain optimal cellular function and energy metabolism by potentially boosting these important cellular molecules.
How Much Vitamin D Do You Need?
The recommended daily allowance (RDA) of vitamin D for people aged 1 through 70 is 600IU (15mcg) daily, and 800IU (20mcg) is recommended for those over 70. Vitamin D status in individuals is monitored with serum 25 (OH) D levels. Optimal levels vary based on stage of life, age, gender, race, and ethnicity. The Food and Nutrition Board of the National Academies (formerly the Institute of Medicine [IOM]) established an upper limit for vitamin D intake of 4,000IU (100mcg)/day. In some cases, higher doses may be suggested based on individual needs.
Vitamin D in Excess
Excess amounts of vitamin D can be toxic, which results in marked hypercalcemia because vitamin D increases calcium absorption in the GI tract.16 Extreme cases of vitamin D toxicity can cause renal failure, calcification of soft tissues throughout the body (including coronary vessels and heart valves), cardiac arrhythmia, and even death. Toxicity may be caused by vitamin D supplements that have high doses of vitamin D that were taken excessively or incorrectly.16 The Food and Nutrition Board established upper limits (UL) for vitamin D in 2010, acknowledging that symptoms of toxicity are unlikely at daily intakes <10,000 IU (250 mcg). Their recommendation for serum vitamin D levels is lower than 125-150 nmol/L (50-60 ng/ml) .17
Summarizing Vitamin D and the Immune System
The immune system is complex and involves many nutrients in addition to vitamin D to function optimally. The information above highlights that vitamin D has a wide range of impacts on the immune system, including modulation of immune response, inflammation, and the gut microbiome. This information suggests vitamin D supplementation may be beneficial for supporting immune health. It is recommended to speak to your healthcare provider when deciding whether to supplement with vitamin D.
References:
- Charoenngam, N. & Holick, M. F. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients 12, 2097 (2020).
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Prietl, B., Treiber, G., Pieber, T. R. & Amrein, K. Vitamin D and Immune Function. Nutrients 5, 2502–2521 (2013).
-
Wei, R. & Christakos, S. Mechanisms Underlying the Regulation of Innate and Adaptive Immunity by Vitamin D. Nutrients 7, 8251–8260 (2015).
-
Holick, M. F. Vitamin D Deficiency. N. Engl. J. Med. 357, 266–281 (2007).
-
Barlow, P. G. et al. Antiviral Activity and Increased Host Defense against Influenza Infection Elicited by the Human Cathelicidin LL-37. Plos One 6, e25333 (2011).
-
Tripathi, S. et al. The human cathelicidin LL-37 inhibits influenza A viruses through a mechanism distinct from that of surfactant protein D or defensins. J Gen Virol 94, 40–49 (2013).
-
Akpınar Ş, Karadağ MG. Is Vitamin D Important in Anxiety or Depression? What Is the Truth? Current Nutrition Reports [Internet]. 2022 Sep 13;11(4). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9468237/
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de la Guía-Galipienso F, Martínez-Ferran M, Vallecillo N, Lavie CJ, Sanchis-Gomar F, Pareja-Galeano H. Vitamin D and cardiovascular health. Clinical Nutrition. 2021 May;40(5):2946–57.
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Vitamin D for heart health: where the benefits begin and end | NHLBI, NIH [Internet]. www.nhlbi.nih.gov. Available from: https://www.nhlbi.nih.gov/news/2022/vitamin-d-heart-health-where-benefits-begin-and-end
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Anjum I, Jaffery SS, Fayyaz M, Samoo Z, Anjum S. The Role of Vitamin D in Brain Health: A Mini Literature Review. Cureus [Internet]. 2018 Jul 10;10(7). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6132681/
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Cui X, Eyles DW. Vitamin D and the Central Nervous System: Causative and Preventative Mechanisms in Brain Disorders. Nutrients [Internet]. 2022 Jan 1;14(20):4353. Available from: https://www.mdpi.com/2072-6643/14/20/4353
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Shi Y, Shi Y, Jie R, He J, Luo Z, Li J. Vitamin D: The crucial neuroprotective factor for nerve cells. Neuroscience [Internet]. 2024 Dec;560:272–85. Available from: https://pubmed.ncbi.nlm.nih.gov/39343160/
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Wrzosek M, Łukaszkiewicz J, Wrzosek M, Jakubczyk A, Matsumoto H, Piątkiewicz P, et al. Vitamin D and the central nervous system. Pharmacological Reports. 2013 Mar;65(2):271–8.
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vitamin D deficiency symptoms (and 10 high vitamin D foods) | University Health Center | Nebraska [Internet]. Unl.edu. 2024. Available from: https://health.unl.edu/9-vitamin-d-deficiency-symptoms-and-10-high-vitamin-d-foods/
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Webb A, Kazantzidis A, Kift R, Farrar M, Wilkinson J, Rhodes L. Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes. Nutrients [Internet]. 2018 Apr 7;10(4):457. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5946242/
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Galior, K., Grebe, S. & Singh, R. Development of Vitamin D Toxicity from Overcorrection of Vitamin D Deficiency: A Review of Case Reports. Nutrients 10, 953 (2018).
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Ross & AC. Institute of Medicine (US) Committee to Review DRIs for Vitamin D and Calcium. (2011).