Vitamin D, also known as calciferol, is a fat-soluble vitamin crucial for overall health. It’s naturally present in limited foods, added to others, and available as a dietary supplement. Our bodies can also produce it when sunlight’s ultraviolet (UV) rays strike the skin, triggering vitamin D synthesis. Understanding How Much Vitamin D Should We Take Daily is essential for maintaining optimal health.
Vitamin D obtained from sun exposure, food, and supplements is biologically inactive and requires two hydroxylations in the body to become active. The liver performs the first hydroxylation, converting vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. The second hydroxylation occurs mainly in the kidney, forming the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], or calcitriol [1].
Vitamin D plays a vital role in:
- Calcium Absorption: Promoting calcium absorption in the gut.
- Bone Health: Maintaining adequate serum calcium and phosphate concentrations for normal bone mineralization, preventing hypocalcemic tetany, and supporting bone growth and remodeling [1-3].
- Overall Health: Reducing inflammation and modulating cell growth, neuromuscular and immune function, and glucose metabolism [1-3].
Insufficient vitamin D can lead to thin, brittle, or misshapen bones, causing rickets in children and osteomalacia in adults. Alongside calcium, it also protects older adults from osteoporosis. Many tissues have vitamin D receptors, and some convert 25(OH)D to 1,25(OH)2D, highlighting its widespread influence.
Vitamin D rich foods can help you reach your recommended daily intake. Focus on incorporating these into your diet.
Understanding Vitamin D Forms and Measurement
Vitamin D exists in two primary forms in food and supplements: D2 (ergocalciferol) and D3 (cholecalciferol). Both are well-absorbed in the small intestine through passive diffusion and carrier proteins [4]. Fat enhances absorption, but it occurs even without dietary fat. Age and obesity don’t alter vitamin D absorption [4].
Serum concentration of 25(OH)D is the key indicator of vitamin D status, reflecting both endogenous production and intake from food and supplements [1]. It has a half-life of 15 days in serum [1]. Serum 25(OH)D concentrations are reported in nanomoles per liter (nmol/L) and nanograms per milliliter (ng/mL), where 1 nmol/L = 0.4 ng/mL, and 1 ng/mL = 2.5 nmol/L.
Assessing vitamin D status is complex due to variability in laboratory assays [5,6]. The international Vitamin D Standardization Program aims to improve measurement accuracy [5,7-10]. Circulating 1,25(OH)2D is not a reliable indicator of vitamin D status because of its short half-life and tight regulation by parathyroid hormone, calcium, and phosphate [1,2].
Optimal Serum Concentrations
While 25(OH)D serves as an exposure biomarker, its role as an effect biomarker on health isn’t fully clear [1,3]. Researchers haven’t definitively linked specific 25(OH)D concentrations to deficiency, bone health adequacy, or overall health.
The Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine (NASEM) suggests:
- Deficiency Risk: <30 nmol/L (<12 ng/mL) [1].
- Potential Inadequacy Risk: 30 to 50 nmol/L (12–20 ng/mL).
- Sufficiency: ≥50 nmol/L (≥20 ng/mL) for most people.
- Adverse Effects Risk: >125 nmol/L (>50 ng/mL) [1].
Understanding your vitamin D levels through testing can help you determine if supplementation is necessary.
Recommended Daily Vitamin D Intakes
The Dietary Reference Intakes (DRIs) developed by NASEM provide intake recommendations [1]. These values vary by age and sex and include:
- Recommended Dietary Allowance (RDA): Meets the nutrient requirements of nearly all (97%–98%) healthy individuals.
- Adequate Intake (AI): Ensures nutritional adequacy when evidence is insufficient for an RDA.
- Estimated Average Requirement (EAR): Meets the requirements of 50% of healthy individuals.
- Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
The FNB established RDAs for vitamin D based on maintaining bone health and normal calcium metabolism, assuming minimal sun exposure [1]. For infants, the FNB developed AIs based on maintaining serum 25(OH)D levels above 20 ng/mL (50 nmol/L) and supporting bone development.
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| 0-12 months* | 10 mcg (400 IU) | 10 mcg (400 IU) | ||
| 1–13 years | 15 mcg (600 IU) | 15 mcg (600 IU) | ||
| 14–18 years | 15 mcg (600 IU) | 15 mcg (600 IU) | 15 mcg (600 IU) | 15 mcg (600 IU) |
| 19–50 years | 15 mcg (600 IU) | 15 mcg (600 IU) | 15 mcg (600 IU) | 15 mcg (600 IU) |
| 51–70 years | 15 mcg (600 IU) | 15 mcg (600 IU) | ||
| >70 years | 20 mcg (800 IU) | 20 mcg (800 IU) |
*Adequate Intake (AI)
Other countries and professional societies may have different guidelines due to incomplete understanding, different purposes for guidelines, and the use of observational studies [9,15]. For example, the UK Scientific Advisory Committee on Nutrition recommends 10 mcg (400 IU)/day for individuals aged 4 and older [16]. The Endocrine Society recommends routine vitamin D supplementation for specific groups but advises adhering to the RDA [11,12].
Food Sources of Vitamin D
Few foods naturally contain vitamin D. The best sources include fatty fish (trout, salmon, tuna, mackerel) and fish liver oils [17,1]. The amount of vitamin D in animal tissues depends on their diet. Beef liver, egg yolks, and cheese contain small amounts, mainly as vitamin D3 and its metabolite 25(OH)D3. Mushrooms provide variable amounts of vitamin D2, especially when UV-treated [17,18].
Animal-based foods also provide 25(OH)D, which is more potent than the parent vitamin [17,[20],21]. Fortified foods, like milk (about 3 mcg/cup or 120 IU), plant milk alternatives, and breakfast cereals, contribute significantly to vitamin D intake [[1],22-24]. Infant formula is also fortified with vitamin D [1].
| Food | Micrograms (mcg) per serving | International Units (IU) per serving | Percent DV* |
|---|---|---|---|
| Cod liver oil, 1 tablespoon | 34.0 | 1,360 | 170 |
| Trout (rainbow), farmed, cooked, 3 ounces | 16.2 | 645 | 81 |
| Salmon (sockeye), cooked, 3 ounces | 14.2 | 570 | 71 |
| Mushrooms, white, raw, sliced, exposed to UV light, ½ cup | 9.2 | 366 | 46 |
| Milk, 2% milkfat, vitamin D fortified, 1 cup | 2.9 | 120 | 15 |
| Soy, almond, and oat milks, vitamin D fortified, various brands, 1 cup | 2.5–3.6 | 100–144 | 13–18 |
| Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 1 serving | 2.0 | 80 | 10 |
| Sardines (Atlantic), canned in oil, drained, 2 sardines | 1.2 | 46 | 6 |
| Egg, 1 large, scrambled** | 1.1 | 44 | 6 |
| Liver, beef, braised, 3 ounces | 1.0 | 42 | 5 |
| Tuna fish (light), canned in water, drained, 3 ounces | 1.0 | 40 | 5 |
| Cheese, cheddar, 1.5 ounce | 0.4 | 17 | 2 |
| Mushrooms, portabella, raw, diced, ½ cup | 0.1 | 4 | 1 |
| Chicken breast, roasted, 3 ounces | 0.1 | 4 | 1 |
| Beef, ground, 90% lean, broiled, 3 ounces | 0 | 1.7 | 0 |
| Broccoli, raw, chopped, ½ cup | 0 | 0 | 0 |
| Carrots, raw, chopped, ½ cup | 0 | 0 | 0 |
| Almonds, dry roasted, 1 ounce | 0 | 0 | 0 |
| Apple, large | 0 | 0 | 0 |
| Banana, large | 0 | 0 | 0 |
| Rice, brown, long-grain, cooked, 1 cup | 0 | 0 | 0 |
| Whole wheat bread, 1 slice | 0 | 0 | 0 |
| Lentils, boiled, ½ cup | 0 | 0 | 0 |
| Sunflower seeds, roasted, ½ cup | 0 | 0 | 0 |
| Edamame, shelled, cooked, ½ cup | 0 | 0 | 0 |
* DV = Daily Value. The FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin D is 20 mcg (800 IU) for adults and children age 4 years and older [26]. The labels must list vitamin D content in mcg per serving and have the option of also listing the amount in IUs in parentheses. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet. ** Vitamin D is in the yolk.
Vitamin D from Sun Exposure
Sunlight exposure is a significant source of vitamin D for many. UVB radiation converts cutaneous 7-dehydrocholesterol to previtamin D3, which becomes vitamin D3. Factors like season, time of day, skin melanin content, and sunscreen affect UV radiation exposure and vitamin D synthesis. Older people and those with darker skin produce less vitamin D from sunlight [1]. UVB radiation does not penetrate glass [27].
It’s difficult to provide precise guidelines on sun exposure due to varying factors [15,28]. Some experts suggest 5–30 minutes of sun exposure between 10 a.m. and 4 p.m., daily or at least twice a week, to the face, arms, hands, and legs without sunscreen [13,15,28]. Moderate use of commercial tanning beds is also effective [13,29].
However, limiting sun exposure to reduce skin cancer risk is prudent [28,30]. Sunscreens with an SPF of 8 or more block vitamin D-producing UV rays, but typical sunscreen use likely allows some vitamin D synthesis [1,28].
Vitamin D Supplements
Supplements contain vitamins D2 or D3. Vitamin D2 is made using UV irradiation of ergosterol in yeast, and vitamin D3 is produced with irradiation of 7-dehydrocholesterol from lanolin or sourced from lichen [13,[31],32].
Both D2 and D3 raise serum 25(OH)D levels and can cure rickets [4]. However, vitamin D3 generally increases serum 25(OH)D levels to a greater extent and maintains them longer than vitamin D2 [33-36]. Supplements containing 25(OH)D3 are more potent per microgram dose but are not widely available [[37],38,32].
Vitamin D Intakes and Status in the US Population
Most Americans consume less than the recommended amounts of vitamin D. Data from the 2015–2016 NHANES show average daily intakes from foods and beverages were 5.1 mcg (204 IU) in men, 4.2 mcg (168 IU) in women, and 4.9 mcg (196 IU) in children age 2–19 years [39]. From 2013–2016, 92% of men, over 97% of women, and 94% of people age 1 year and older ingested less than the EAR of 10 mcg (400 IU) of vitamin D from food and beverages [40].
In 2015–2016, 28% of individuals age 2 years and older took a vitamin D supplement [39]. Supplement use increased with age, with total vitamin D intakes three times higher with supplement use. Some people take very high doses; in 2013–2014, 3.2% of U.S. adults took supplements containing 100 mcg (4,000 IU) or more [41].
Serum 25(OH)D levels are influenced by sun exposure and 25(OH)D from animal foods [[1],42]. NHANES 2011–2014 data showed that most U.S. individuals age 1 year and older had sufficient vitamin D intakes according to FNB thresholds [43]. However, 18% were at risk of inadequacy, and 5% were at risk of deficiency. Deficiency rates varied by race and ethnicity.
Vitamin D Deficiency: Causes and Consequences
Vitamin D deficiency can arise from inadequate intake, limited sun exposure, impaired kidney conversion of 25(OH)D, or poor absorption. Diets low in vitamin D are more common in people with milk allergies, lactose intolerance, or those following ovo-vegetarian or vegan diets [1].
In children, vitamin D deficiency leads to rickets, causing soft bones and skeletal deformities [44]. Severe rickets can result in failure to thrive, developmental delay, seizures, muscle spasms, cardiomyopathy, and dental abnormalities [[45],46].
Rickets, caused by vitamin D deficiency, leads to bone deformities in children. Supplementation is crucial for prevention.
Prolonged exclusive breastfeeding without vitamin D supplementation can cause rickets, especially in Black infants [47]. While milk fortification and cod liver oil made rickets rare, its incidence is increasing globally, particularly among immigrants [[28],[50],51], due to genetic differences, dietary preferences, and behaviors leading to less sun exposure [[45],46].
In adults and adolescents, deficiency can lead to osteomalacia, resulting in weak bones [46]. Signs and symptoms are similar to rickets [45]. Routine screening for vitamin D status is becoming more common, but the USPSTF found insufficient evidence to assess its benefits and harms in asymptomatic adults [[6],52-55].
Groups at Risk of Vitamin D Inadequacy
Breastfed Infants
Human milk alone doesn’t meet infant vitamin D requirements [[1],[56],57]. The AAP recommends 10 mcg (400 IU)/day vitamin D supplements for exclusively and partially breastfed infants starting shortly after birth until they consume sufficient vitamin D-fortified formula or whole milk [[57],59].
Older Adults
Older adults are at increased risk due to decreased skin synthesis capacity and spending more time indoors [[1],61].
People with Limited Sun Exposure
Homebound individuals, those who wear concealing clothing, and people with limited sun exposure are unlikely to get adequate vitamin D from sunlight [62]. Sunscreen use also limits synthesis.
People with Dark Skin
Higher melanin levels reduce the skin’s ability to produce vitamin D from sunlight [1].
People with Conditions Limiting Fat Absorption
Vitamin D absorption relies on the gut’s ability to absorb dietary fat [4]. Fat malabsorption from liver disease, cystic fibrosis, celiac disease, Crohn’s disease, and ulcerative colitis increases deficiency risk [[1],63].
People with Obesity or Who Have Undergone Gastric Bypass Surgery
Obesity is associated with lower serum 25(OH)D levels due to vitamin D sequestration in subcutaneous fat [[1],[64],65]. Gastric bypass surgery can also lead to deficiency by bypassing the vitamin D absorption site [[66],67].
Health Risks from Excessive Vitamin D
Excessive vitamin D intake leads to hypercalcemia, hypercalciuria, and high serum 25(OH)D levels [158]. Hypercalcemia can cause nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, dehydration, and kidney stones.
In extreme cases, toxicity causes renal failure, soft tissue calcification, cardiac arrhythmias, and death. It is typically caused by manufacturing errors, inappropriate use of supplements, or incorrect prescriptions [158-160]. Excessive sun exposure is unlikely to cause toxicity, but frequent use of tanning beds can [[1],161-163].
The FNB established ULs for vitamin D, recommending avoidance of serum 25(OH)D levels above approximately 125–150 nmol/L (50–60 ng/mL) due to potential adverse health effects [1].
| Age | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| 0–6 months | 25 mcg (1,000 IU) | 25 mcg (1,000 IU) | ||
| 7–12 months | 38 mcg (1,500 IU) | 38 mcg (1,500 IU) | ||
| 1–3 years | 63 mcg (2,500 IU) | 63 mcg (2,500 IU) | ||
| 4–8 years | 75 mcg (3,000 IU) | 75 mcg (3,000 IU) | ||
| 9–18 years | 100 mcg (4,000 IU) | 100 mcg (4,000 IU) | 100 mcg (4,000 IU) | 100 mcg (4,000 IU) |
| 19+ years | 100 mcg (4,000 IU) | 100 mcg (4,000 IU) | 100 mcg (4,000 IU) | 100 mcg (4,000 IU) |
Interactions with Medications
Vitamin D supplements can interact with medications, including:
- Orlistat: Reduces vitamin D absorption [167-170].
- Statins: May reduce vitamin D synthesis, and high vitamin D intakes may reduce statin potency [170-173].
- Steroids: Reduce calcium absorption and impair vitamin D metabolism [174-177].
- Thiazide Diuretics: Increase risk of hypercalcemia when combined with vitamin D supplements [[170],[178],179].
Discuss vitamin D intakes and status with healthcare providers when taking these medications.
Conclusion: Determining Your Optimal Daily Vitamin D Intake
Understanding how much vitamin D should we take daily is crucial for maintaining bone health, immune function, and overall well-being. While sunlight exposure and fortified foods contribute to vitamin D levels, many individuals may require supplementation to meet their needs. Factors such as age, skin pigmentation, geographical location, and underlying health conditions influence individual vitamin D requirements.
Consult with a healthcare professional to assess your vitamin D status and determine the most appropriate daily intake based on your specific needs. By adopting a proactive approach to vitamin D management, you can optimize your health and quality of life.
