Vitamin D is unique in that it is both a nutrient we eat and a hormone our bodies make. Research has suggested adequate vitamin D may help with bone health and muscle strength, help to prevent depression, prevent some types of cancers, treat heart disease and type 2 diabetes and help create a strong immune system.

Studies have shown in the US alone, 42% of adults are deficient in vitamin D, while 50% of children aged between one and five and 70% of children aged between six and 11 have low vitamin D stores. The statistics are even higher for people with dark skin. Nearly 63% of Hispanic adults and 82% of African American adults are vitamin D deficient.

Food Sources of Vitamin D

Few foods are naturally rich in vitamin D3. The best sources are the flesh of fatty fish and fish liver oils. Smaller amounts are found in egg yolks, cheese, and beef liver. Certain mushrooms contain some vitamin D2; in addition, some commercially sold mushrooms contain higher amounts of D2 due to intentionally being exposed to high amounts of ultraviolet light. Many foods and supplements are fortified with vitamin D like dairy products and cereals.

• Cod liver oil
• Salmon
• Swordfish
• Tuna fish
• Orange juice fortified with vitamin D
• Dairy and plant milks fortified with vitamin D
• Sardines
• Beef liver
• Egg yolk
• Fortified cereals

Note: Almost all of the U.S. milk supply is fortified with about 3 mcg (120 IU) vitamin D per cup. Many plant-based alternatives such as soy milk, almond milk, and oat milk are similarly fortified.

How Much Vitamin D Do You Need Each Day?

The Recommended Dietary Allowance for vitamin D provides the daily amount needed to maintain healthy bones and normal calcium metabolism in healthy people. It assumes minimal sun exposure.

RDA: The Recommended Dietary Allowance for adults 19 years and older is 600 IU (15 mcg) daily for men and women, and for adults >70 years it is 800 IU (20 mcg) daily.

UL: The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for vitamin D for adults and children ages 9+ is 4,000 IU (100 mcg).

The amount of vitamin D you need each day depends on your age. Average daily recommended amounts are listed below in micrograms (mcg) and International Units (IU):

Life Stage	Recommended Amount
Birth to 12 months	10 mcg (400 IU)
Children 1–13 years	15 mcg (600 IU)
Teens 14–18 years	15 mcg (600 IU)
Adults 19–70 years	15 mcg (600 IU)
Adults 71 years and older	20 mcg (800 IU)
Pregnant and breastfeeding teens and women	15 mcg (600 IU)

Vitamin D from the Sun

Vitamin D3 can be formed when a chemical reaction occurs in human skin, when a steroid called 7-dehydrocholesterol is broken down by the sun’s UVB light or so-called “tanning” rays. The amount of the vitamin absorbed can vary widely.

The following are conditions that decrease exposure to UVB light and therefore lessen vitamin D absorption:

• Use of sunscreen; correctly applied sunscreen can reduce vitamin D absorption by more than 90%.
• Wearing full clothing that covers the skin.
• Spending limited time outdoors.
• Darker skin tones due to having higher amounts of the pigment melanin, which acts as a type of natural sunscreen.
• Older ages when there is a decrease in 7-dehydrocholesterol levels and changes in skin, and a population that is likely to spend more time indoors.
• Certain seasons and living in northern latitudes above the equator where UVB light is weaker. The body stores vitamin D from summer sun exposure, but it must last for many months. By late winter, many people in these higher-latitude locales are deficient.

Note that because ultraviolet rays can cause skin cancer, it is important to avoid excessive sun exposure and in general, tanning beds should not be used.

Adequate Vitamin D and Your Health

Research has suggested adequate vitamin D may help prevent or treat these following health issues:

1. Bone health and muscle strength.
2. Helps to treat osteoporosis.
3. May help to prevent depression.
4. May help prevent some types of cancers.
5. Help treat heart disease and type 2 diabetes.
6. Help create a strong immune system.
7. May help prevent premature deaths.
8. May help with cognitive decline like dementia.

How Does a Vitamin D Deficiency Occur

Vitamin D deficiency may occur from a lack in the diet, poor absorption, or having a metabolic need for higher amounts. If you are not eating enough vitamin D and you don’t receive enough ultraviolet sun exposure over an extended period, you may become deficient in Vitamin D. People who cannot tolerate or do not eat milk, eggs, and fish, such as those with a lactose intolerance or who follow a vegan diet, are at higher risk for a deficiency. Other people at high risk of vitamin D deficiency include:

• People with inflammatory bowel disease (ulcerative colitis, Crohn’s disease) or other conditions that disrupt the normal digestion of fat. Vitamin D is a fat-soluble vitamin that depends on the gut’s ability to absorb dietary fat.
• People who are obese tend to have lower blood vitamin D levels. Vitamin D accumulates in excess fat tissues but is not easily available for use by the body when needed. Higher doses of vitamin D supplementation may be needed to achieve a desirable blood level. Conversely, blood levels of vitamin D rise when obese people lose weight.
• People who have undergone gastric bypass surgery, which typically removes the upper part of the small intestine where vitamin D is absorbed.

Medical Conditions Resulting from Prolonged Vitamin D Deficiency

• Rickets: A condition in infants and children of soft bones and skeletal deformities caused by failure of bone tissue to harden.
• Osteomalacia: A condition in adults of weak and softened bones that can be reversed with supplementation. This is different than osteoporosis, in which the bones are porous and brittle and the condition is irreversible.

 

Who Needs Vitamin D Supplements?

Vegans have low vitamin D levels because they avoid foods that are rich in vitamin D — including meat, fish, egg yolks, and dairy products that have been fortified with the vitamin. One 2016 study found vitamin D serum concentration was 34 percent lower among study participants who followed a vegan diet compared with those who ate meat and dairy.

Vegans should drink plant milk beverages, such as those made from soy, oats, and almond, are often fortified with vitamin D to the level found in fortified cow’s milk (about 100 IU/cup), according to the National Institutes of Health. 

People with obesity also may need a vitamin D supplement. Research has suggested the possible reasons for deficiency include a lower dietary intake of vitamin D among obese men compared with nonobese men and women, the possibility that obese people expose less skin to the sun (not due to poorer absorption alone), and a decrease in the absorption rate of vitamin D among people who’ve had bariatric or gastric bypass procedures.

As for older people, might need a supplement because they spend more time indoors but also because the process of synthesizing vitamin D from food or sunshine becomes less efficient as people age, according to past research.

What is the Difference Between Vitamin D2 and Vitamin D3 Supplements?

Vitamin D2 is made from plants and is found in fortified foods and some supplements. Vitamin D3 is naturally produced in the human body and also found in animal foods. A meta-analysis of randomized controlled trials which compared vitamin D2 with vitamin D3 supplements found D3 supplements raised the blood concentrations of vitamin D more and those levels were sustained longer than D2.

Vitamin D supplements may interact with some medicines.

Here are several examples of medicines and Vitamin D interactions:

• Orlistat (Xenical® and alli®) is a weight-loss drug. It can reduce the amount of vitamin D your body absorbs from food and supplements.
• Cholesterol-lowering stating might not work as well if you take high-dose vitamin D supplements. This includes atorvastatin (Lipitor®), lovastatin (Altoprev® and Mevacor®), and simvastatin (FloLipid™ and Zocor®)
• Steroids such as prednisone (Deltasone®, Rayos®, and Sterapred®) can lower your blood levels of vitamin D.
• Diuretics (such as Hygroton®, Lozol®, and Microzide®) could raise your blood calcium level too high if you take vitamin D supplements.

 

Too Much Vitamin D Can Lead to a Toxicity

Since Vitamin D is a fat-soluble vitamin, you can get too much vitamin D. Vitamin D toxicity happens from taking supplements. Some people think if some is good more is better.  The low amounts of the vitamin found in food are unlikely to reach a toxic level, and a high amount of sun exposure does not lead to toxicity because excess heat on the skin prevents D3 from forming. It is advised to not take daily vitamin D supplements containing more than 4,000 IU unless monitored under the supervision of your doctor.

Symptoms of toxicity:

• Anorexia
• Weight loss
• Irregular heart beat
• Hardening of blood vessels and tissues due to increased blood levels of calcium, potentially leading to damage of the heart and kidneys

From: NIH.gov/factsheets/VitaminD-Consumer/.