What Is the Best Vitamin D Dosage for Men and Women?

Vitamin D is a fat soluble vitamin that has several functions in the body. The best vitamin D dosage for men and women is 400 IU per day, but it is 800 IU per day for men and women over 70.

Vitamins are micronutrients that you will frequently get from your food. Vitamin D is unusual among vitamins — your body can produce it on its own if it is exposed to ultraviolet radiation, but often not in sufficient quantities. Vitamin D dosage will also vary depending on whether you are meeting daily requirements or treating established deficiencies. It's important to get vitamin D dosage right because it is not water-soluble, so an overdose can be very dangerous.

Two forms of vitamin D can be found externally in nature. Vitamin D2 is also called ergocalciferol and is mostly found in mushrooms and other plant sources. Vitamin D3 is called cholecalciferol and is found in animal-sourced foods like fish, eggs, and milk. Both forms are absorbed from the small intestine and require chemical alteration before they become biologically active.

Vitamin D (also known as calciferol) is a fat-soluble vitamin, like vitamin A, vitamin E, and vitamin K. Your food usually contains only small amounts of this vitamin. Fortunately, your body has a metabolic pathway to generate this vitamin from cholesterol in the presence of sunlight. This reaction occurs in the skin, with skin color, length of sun exposure, and the strength and availability of sunlight all affecting vitamin D production.

This vitamin has several functions in the body:

• Affecting absorption of calcium and phosphorus from the intestines
• Promoting deposition of calcium in the bones (mineralization)
• Strengthening the immune system
• Reducing inflammation
• Minimizing infections
• Reducing cancer cell growth

The vitamin D obtained from food or sunlight is initially inactive. Activation follows hydroxylation in the liver and the kidneys. The activated vitamin D is called calcitriol or 25-dihydroxycholecalciferol.

When trying to get vitamin D by exposing your skin to sunlight, though, be careful to avoid sunburn. Fortunately, the time needed to generate enough vitamin D is less than the time required for sunburn, so enjoy the sun safely and get your vitamin D without increasing your risk of skin cancer.

Adult men and women should both receive the same amounts of vitamin D. The estimated average requirement (EAR) is 400 international units (or, 10 micrograms) per day, and the recommended dietary allowance (RDA) is 600 IU (15 micrograms) per day. However, for women and men over 70, the RDA is 800 IU (20 micrograms) per day. RDAs are the levels of intake of essential nutrients that are adequate to meet the needs of most healthy persons.

Vitamin D dosage recommendations often vary, though. The Endocrine Society recommends a daily intake of 1,500 to 2,000 IU (37.5 to 50 micrograms) a day. The U.K government recommends only 400 IU (10 micrograms) a day of vitamin D for all people over the age of 4 years.

It is difficult to meet the daily requirements of vitamin D through food, even though several foods, like fruit juices and breakfast cereals, are fortified with vitamin D. Enough exposure to the sun might help you synthesize your daily vitamin D, but darker skin, distance from the equator, clothes that fully cover the skin, sunscreen, older age, lack of time outside, and shorter days can all reduce vitamin D production in the body, leaving some at risk of vitamin D deficiency.

Good natural sources of vitamin D include:

• Cod liver oil
• Salmon, tuna, sardines, and swordfish
• Beef liver
• Egg yolk

Additionally, almost everyone gets enough vitamin D during the summer months. Most people should take supplements when sunlight is scarce during autumn and winter, though. Pregnant and breastfeeding people should also take supplements, as well as people at risk of deficiency.

If you believe you are not getting enough vitamin D, speak with your doctor about a recommended supplemental amount.

Deficiency of this vitamin can occur because your intake is insufficient, you're not able to absorb it, or your needs are higher. Those with clinical vitamin D deficiency may include: 

• People with digestive disorders. Those with issues like inflammatory bowel disease, Crohn's disease, ulcerative colitis, etc. may be at risk of malabsorption syndromes.
• People with restricted diets. People who don't eat eggs, fish, and milk products may get no dietary vitamin D. People following vegan diets are often at risk.
• People who have had bariatric surgery. Such surgery often removes the upper part of the small intestine. This is the part that absorbs vitamin D.
• People who are at work or otherwise indoors during daylight hours. Window glass blocks ultraviolet B light, which your skin needs to convert cholesterol to vitamin D.

Vitamin D deficiency in children produces a clinical disorder called rickets. Affected children may have bone pain, deformities, failure to thrive, developmental delay, seizures, tooth abnormalities, and heart muscle disease (cardiomyopathy).

In adults, vitamin D deficiency can result in osteomalacia. Bones become weak, resulting in deformities and widespread pain. Other symptoms include tooth abnormalities, seizures, and spasms. You might also have muscle aches and weakness, a waddling gait, and bony pain in the lower back, pelvis, and feet.

Your doctor can detect vitamin D deficiency by measuring blood levels, which indicate the following:

• Less than 12 nanograms per milliliter: vitamin D deficiency
• 12 to 20 nanograms per milliliter: inadequate bone health
• More than 20 nanograms per milliliter: sufficient bone health
• More than 50 nanograms per milliliter: possibility of adverse effects

If you have any symptoms of vitamin D deficiency, you should meet your healthcare provider. Treatment of established deficiency requires high-dose preparations of the vitamin that aren't available over the counter. Your doctor will probably prescribe 50,000 IU (1,250 micrograms) every week for six weeks, followed by a daily vitamin D dose of 800 IU (20 micrograms).

If your vitamin D deficiency has occurred because of intestinal disorders, you will need different treatments. Since you can't absorb vitamin D taken by mouth, your doctor will prescribe ergocalciferol injections. A single dose of 300,000 IU is usually administered. Your doctor will decide on further doses after testing your blood levels again.

Some vitamins, like vitamin C and B group vitamins, are water-soluble. The kidneys easily remove excessive amounts in the urine. However, vitamin D is a fat-soluble vitamin. If you take too much, it'll accumulate in your body. Too much vitamin D leads to over-accumulation of calcium (hypercalcemia), which weakens your bones and may damage your kidneys and heart.

Consult a doctor if you believe you would benefit from vitamin D supplements, but take only the recommended daily allowance (RDA). Taking more may be harmful.