Key Takeaways
It may be best to take vitamin D in the morning because taking it at night might reduce melatonin production. Most foods do not have enough vitamin D to meet people’s needs, so supplements can help fill the gap.Consider taking vitamin D during darker months when the sun is less intense.
Taking vitamin D in the morning is most beneficial, as evening intake may interfere with melatonin production and impact sleep quality. For most adults, a daily dose of 600 IU to 800 IU is typically recommended; however, individual needs may vary.
How Timing Affects Vitamin D Absorption
Research suggests that taking vitamin D in the morning may be more effective than in the evening, as evening intake can reduce melatonin production. Melatonin helps you feel sleepy, while vitamin D and melatonin work in opposition. Sun exposure affects your vitamin D levels, which in turn regulate melatonin production.
Your circadian rhythm, the internal clock for wakefulness and sleep, may help control vitamin D levels. Studies indicate that these levels change with the time of day and sun exposure. Vitamin D levels are typically higher in areas with more sun exposure. Conversely, melatonin production increases when there’s less sunlight, such as during winter or at higher latitudes.
Overall, your vitamin D levels can influence your sleep, with low levels contributing to poor sleep quality and duration. While your body absorbs vitamin D within 24 hours, peak levels typically occur 7 to 14 days after supplementation.
Additional research is needed to understand the interaction between vitamin D and your circadian rhythm, as well as whether this influences the optimal time of day for supplementation.
Are You Getting Enough Vitamin D Daily?
Vitamin D has a recommended dietary allowance (RDA), which indicates the average daily amount needed to meet nutritional requirements.
RDA for Adults
RDA in International Units (IU) and Micrograms (mcg)
Adults age 18 to 70
600 IU (15 mcg)
Adults age 71 and older
800 IU (20 mcg)
Pregnant and lactating people
600 IU (15 mcg)
Know your tolerable upper limit (UL) for vitamin D to avoid potential toxicity from excess intake. Consider your food, sunlight exposure, and supplements, including multivitamins, when evaluating your vitamin D intake.
Recommended amount: The amount of vitamin D for healthy adults to take from supplements generally considered safe is up to 1,000 to 2,000 IUs per day.Tolerable upper limit: The UL represents the maximum daily amount of a vitamin that is unlikely to cause adverse health effects. The upper limit for vitamin D for all adults 18 and older is 4,000 IU (100 micrograms).Toxicity: Too much vitamin D is toxic because it affects calcium in the body. Excessive vitamin D intake can lead to very high calcium levels, which may cause vomiting, muscle weakness, dehydration, and kidney stones, among other symptoms. In severe cases, vitamin D toxicity causes kidney failure, irregular heartbeat, soft tissue calcification, and even death. Vitamin D toxicity occurs from regularly taking high-dose vitamin D supplements.
Choosing Good Sources of Vitamin D
Food Sources of Vitamin D
Some foods naturally contain vitamin D, whereas others are fortified. Natural sources of vitamin D include:
Cod liver oil (450 IU per teaspoon)Farmed rainbow trout (645 IU per cooked 3-ounce serving)Mushrooms (0.4 IU per cup of sliced white mushrooms)Sardines (180 IU per 3.75-ounce can serving)Sockeye salmon (570 IU per cooked 3-ounce serving)
Fortified foods have vitamin D added to boost the nutritional content. Fortified sources of vitamin D include:
Almond milk (105 IU per 8-ounce serving)Breakfast cereals, 2% cow’s milk (110 IU per 8-ounce serving)Orange juice (105 IU per 8-ounce serving)
Soy milk (110 IU per 8-ounce serving)
Supplements
Depending on your current vitamin D levels, you may need a supplement. They come in various dosages, with some exceeding the tolerable upper limit of 4,000 IU per day. Avoid taking more than 4,000 IUs of vitamin D daily unless your healthcare provider advises.
Vitamin D supplements are available as ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Some research suggests that vitamin D3 is better at maintaining circulating nutrient levels during the fall and winter. If you live in the northern hemisphere, you may want to consider evaluating your vitamin D levels and possibly supplementing from October through March.
Most multivitamins contain 400 to 600 IU of vitamin D, around the daily amount needed for adults. However, choose a supplement based on your vitamin D blood test results.
Sunlight
Your body makes vitamin D when your skin is exposed to sunlight. Ultraviolet (UV) rays activate vitamin D3 in the skin, turning it into its active form. To get vitamin D from the sun, expose your face, arms, hands, and legs to sunlight between 10 a.m. and 4 p.m. for at least five to 30 minutes, twice a week.
Still, balancing skin damage from the sun with vitamin D production is challenging. Using sunscreen can prevent your body from producing vitamin D.
Who Needs a Vitamin D Supplement?
Specific populations are particularly vulnerable to vitamin D deficiency. Understanding these risks can help inform your dietary choices and the need for supplementation to support your overall health.
People with the following should consider their vitamin D intake and, potentially, a supplement:
Limited sun exposure: Vitamin D levels are impacted by clothing, sunscreen use, latitude, and season. People covering their bodies or using high SPF sunscreens absorb less vitamin D from sunlight. In winter, particularly at latitudes above 37 degrees, decreased sunlight and increased clothing lead to lower vitamin D synthesis. Dark skin pigmentation: Melanin, the compound responsible for skin pigmentation, causes individuals with darker skin to absorb less UV light, making it more challenging to produce vitamin D. Pregnancy: Vitamin D needs are not increased during pregnancy. Most prenatal supplements contain some vitamin D to ensure a pregnant person gets enough.Autism: Some studies suggest that people with autism may have lower vitamin D levels and would benefit from supplementation.At risk of type 1 diabetes: Type 1 diabetes is an autoimmune condition where the pancreas fails to produce insulin. Research suggests that vitamin D may help protect insulin-producing cells. Maintaining adequate vitamin D levels may reduce the risk of developing type 1 diabetes.Type 2 diabetes: Vitamin D supports glucose metabolism, and low levels are linked to an increased risk and progression of type 2 diabetes.Conditions that impact fat or vitamin absorption: Changes to the gastrointestinal tract that affect absorption impact vitamin D levels. People with short bowel disease or inflammatory bowel disease (IBD), such as Crohn’s disease, celiac disease, and, to a lesser extent, ulcerative colitis, tend to have lower circulating vitamin D levels.Gastric bypass surgery: Bariatric surgery (weight loss surgery) changes the structure of the gastrointestinal tract. This affects nutrient absorption.Older adults: The body’s ability to produce vitamin D from the sun decreases with age. Additionally, older adults may be less likely to spend significant time outdoors, especially during peak sun hours. The risk of bone loss increases with age.Obesity: Low vitamin D levels can occur among people living with obesity due to multiple factors, including less time outdoors in the sunlight, reduced vitamin D intake, impaired liver production of vitamin D, and increased storage of vitamin D in fat (adipose) cells.
Vegetarian or vegan diet: A vegetarian or vegan diet may provide inadequate vitamin D, especially if it excludes eggs, dairy, and fortified foods.
Alcohol use disorder (AUD): Vitamin D deficiency is common among people with AUD. Moreover, vitamin D deficiency is a risk factor for liver damage and impaired blood sugar.Specific medications: Taking vitamin D with statin medications that lower cholesterol may reduce the medication’s effectiveness. Thiazide diuretics decrease the removal of calcium from the body. Vitamin D supplements increase calcium absorption, so taking vitamin D with thiazide diuretics may lead to elevated calcium (hypercalcemia).
Supplement use should be individualized and vetted by a healthcare professional, such as a healthcare provider, pharmacist or registered dietitian. No supplement is intended to treat, cure, or prevent disease.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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