Vitamin D is a fat-soluble vitamin that regulates the absorption of calcium and phosphorus as well as facilitates normal immune system function. This vitamin is an essential nutrient important for strong bones. Vitamin D has 2 forms: D2 (obtained from foods you eat) and D3 (obtained from sun exposure). Vitamin D is produced by the body when your skin is exposed to sunlight. You can also get vitamin D through certain foods and supplements. It's important to get enough of this vital nutrient so you don't end up with a vitamin D deficiency.
Benefits of Vitamin D
Your body needs vitamin D to help absorb the calcium and phosphorus in your diet that makes for strong bones. Vitamin D deficiency can cause bone loss, low bone density, and increase your chances of breaking bones. Vitamin D deficiency can also cause rickets in children and a condition called osteomalacia in adults. Symptoms may include weakness and bone pain.
Higher blood levels of vitamin D seem to be associated with a lower risk of developing multiple sclerosis (MS). A recent study shows vitamin D may slow the progression of the disease, though the connection between the vitamin and MS is not clear. It is unknown if low levels of vitamin D cause MS or are a result of the disease. MS is more common in areas north of the equator, suggesting that the amount of sunshine one receives is connected to their likelihood of developing MS. People are less likely to develop MS if they have higher vitamin D levels. Supplementation with vitamin D may be beneficial for MS patients, but the dose is yet to be determined.
Type 2 diabetes is a condition in which the body does not use insulin properly and blood sugar levels can rise above normal. Researchers are looking into whether vitamin D can help regulate blood sugar levels. In addition, vitamin D helps with the absorption of calcium, and calcium helps manage sugar in the blood. Studies have found people with vitamin D deficiency have a higher risk of developing type 2 diabetes later in life, but the link is not conclusive. More research is needed to determine if vitamin D supplementation can help people with type 2 diabetes.
Obesity is a risk factor for low vitamin D levels because the more weight you carry, the more vitamin D your body requires. Studies have also shown vitamin D deficiency may increase your risk of becoming obese later in life. One small study found women with low levels of vitamin D might be more prone to gain weight. Vitamin D and calcium may act as an appetite suppressant as well.
There may be an association between low levels of vitamin D and depression, but studies show mixed results and further research is needed. Vitamin D receptors in the brain have been linked to the development of depression. Vitamin D itself may not ward off depression, but patients who are taking antidepressants along with vitamin D may help reduce symptoms of depression.
The easiest way to get vitamin D is by exposing your skin to direct sunlight, specifically, ultraviolet B (UVB) rays. The more you expose your skin, the more vitamin D your body produces. You only need to spend about half as much time as it takes to turn pink and get sunburn. This means if you are fair-skinned and normally start to turn pink in 30 minutes, you only need 15 minutes of pre-sunscreen sun exposure to produce the vitamin D3 your body needs. The darker your skin, the more time you need in the sun to produce vitamin D. The amount of vitamin D you get from sun exposure depends on the time of day, your skin tone, where you live, and how much skin you expose.
Generally, sun exposure is the best way to get the vitamin D your body needs. Most foods that contain vitamin D only contain small amounts and won't give you the total amount your body needs.
Foods High in Vitamin D
- Fatty fish such as salmon or mackerel
- Beef liver
- Egg yolks
- Orange juice fortified with vitamin D
- Fortified cereals
- Infant formulas
If you are unable to obtain enough vitamin D from sun exposure, there are foods containing this vitamin that can start kick-start your day. Many foods typically eaten for breakfast are fortified with vitamin D. Read labels to find out how much vitamin D is in the food you eat for breakfast.
Breakfast Foods Good for a Vitamin D Boost
- Milk (fortified)
- Cereal (fortified)
- Orange juice (fortified)
- Breads (fortified)
- Yogurt (fortified)
- Egg yolks
If you don't get enough sun exposure, food is unlikely to give you the amount of vitamin D your body needs. In this case, your doctor may recommend you take vitamin D supplements. There are two forms of vitamin D: D2 (ergocalciferol), found in food, and D3 (cholecalciferol), produced by your body from exposure to sunlight. Most over-the-counter vitamin D supplements contain vitamin D3, which is not usually vegetarian. If you have concerns about this, your doctor may prescribe vitamin D2 supplements.
People may be at risk for vitamin D deficiency if they dislike the sun, suffer from milk allergies, or stick to a vegan diet. People with dark skin may also be at risk for developing vitamin D deficiency. This is because the pigment melanin reduces their skin's ability to make vitamin D after sun exposure. Other risk factors for vitamin D deficiency include:
- Covering your skin with clothing or SPF all the time
- Obesity or gastric bypass surgery
- Infants who are breastfed and not given a vitamin D supplement
- Living in northern regions where there are fewer hours of sunlight
- Being older (your skin is thinner)
Vitamin D deficiency symptoms may be very general. You might have aches, pains and fatigue or you may have no symptoms at all. If your vitamin D deficiency is severe, you may suffer from bone pain and reduced mobility. In adults, severe vitamin D deficiency is called osteomalacia, and in children a severe deficiency can lead to rickets (softening and weakening of bones).
A simple blood test called the 25-hydroxy vitamin D test can measure levels of vitamin D in the blood. Levels of the vitamin are measured in nanograms per milliliter (ng/mL). 20 ng/mL to 50 ng/mL is an adequate level for bone and overall health, and a level less than 12 ng/mL indicates vitamin D deficiency. Many experts suggest that higher levels of vitamin D, 35 to 40 ng/ml, are suggested for preventive health. Levels higher than that do not appear to offer any additional benefits.
The U.S. recommended daily allowance (USRDA) for vitamin D is 600 IU (international units) per day for those 1-70 years of age. Infants under 1 year need 400 IU, while adults 71 and older require 800 IU.
The amount of vitamin D in human breast milk is minimal. Since infants should be kept from direct sunlight and use sunscreen, they generally do not get enough of this vitamin without supplementation. The American Academy of Pediatrics (AAP) recommends nursing infants should receive 400 IU of vitamin D supplementation per day. Over-the-counter products, such as multivitamin products, are available to provide vitamin D supplementation for infants.
Many children do not get the recommended amounts of vitamin D in their diet, putting them at risk for vitamin D deficiency and rickets. The American Academy of Pediatrics (AAP) recommends infants 1 year and under get 400 IU per day of vitamin D and 600 IU daily of vitamin D for children and teens. Talk to your child's pediatrician about vitamin D supplementation and the right amount for your child.
There is such a thing as too much vitamin D. Vitamin D in excess of 4,000 IU can cause side effects such as anorexia, excessive urine output, heart arrhythmias, and kidney stones. Excess vitamin D is usually caused by taking too much in the form of supplements. It is not possible to get too much vitamin D from sun exposure – the body regulates the amount it produces.
Vitamin D Overdose Side Effects
Hypervitaminosis D occurs when people take too many vitamin D supplements. When there is too much vitamin D in the body, calcium levels rise and can lead to hypercalcemia. Symptoms of hypercalcemia include:
- Excessive urine output
- Heart arrhythmias
- Excessive thirst
- Muscle weakness
- Vomiting, nausea, and dizziness
- High blood pressure
Organs Damaged by Long-Term Vitamin D Toxicity
- Blood vessels
Vitamin D supplements can interact with several types of medications. Steroids can interfere with vitamin D metabolism and affect calcium absorption. Weight loss drugs including orlistat (Xenical, and Alli) and the cholesterol-lowering drug cholestyramine (Questran, LoCholest, Prevalite) can reduce your body's absorption of vitamin D and other fat-soluble vitamins. Drugs to control epileptic seizures, phenobarbital and phenytoin (Dilantin), can increase the metabolism of vitamin D and reduce calcium absorption. Statins and diuretics can increase vitamin D levels. Tell your doctor if you take any vitamin D supplements.
Some studies have shown that high levels of vitamin D may lower cancer risk. More research is needed to determine if low levels of vitamin D in the blood increase cancer risk, or if adequate supplementation of vitamin D can prevent cancer.
Research is ongoing on the possible connection between certain cancers and vitamin D. Some think it may help prevent colon, prostate, and breast cancers, but the evidence is lacking and it is unknown if vitamin D can prevent cancer, or increase risk. One study even found that low vitamin D levels might increase the risk of pancreatic cancer. Vitamin D and omega-3 fatty acids may reduce risk for developing cancer, heart disease, and stroke.
Low levels of dietary vitamin D are associated with a greater risk for stroke and heart disease. On the flip side, high levels of vitamin D deficiency can cause toxicity and damage the heart, blood vessels, and kidneys. Talk to your doctor about the right amount of vitamin D for your health needs.
One risk factor for lower levels of vitamin D is age. As we age, our skin thins, and we can't produce as much vitamin D as we used to. Low levels of vitamin D have been associated with cognitive decline. Vitamin D may be a very important factor for preventing dementia.
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- American Academy of Cardiology: "More Severe Heart Disease Found in Patients With Vitamin D Deficiency"
- American Academy of Pediatrics: "Vitamin D Supplementation for Infants"
- BioMed Central Journal: "Calcium Plus Vitamin D3 Supplementation Facilitated Fat Loss in Overweight and Obese College Students With Very-Low Calcium Consumption: A Randomized Controlled Trial"
- CDC: "Vitamin D Supplementation"
- JamaNetwork.org: "Vitamin D as an Early Predictor of Multiple Sclerosis Activity and Progression"
- Medscape: "Low Vitamin D in Diet Linked to Increased Stroke", "Vitamin D: A Rapid Review: The "Ideal" Vitamin D Blood Level", "Which is Better: Vitamin D2 OR D3"
- National Center for Biotechnology Information, U.S. National Library of Medicine: "Vitamin D and Risk of Cognitive Decline in Elderly Persons"
- National Institutes of Health, Office of Dietary Supplements: "Dietary Supplement Fact Sheet: Vitamin D", "Vitamin D Fact Sheet for Health Professionals"
- National Multiple Sclerosis Society: "Vitamin D"
- National Osteoporosis Foundation: "Calcium/Vitamin D"
- VitalStudy.org: "The Vitamin D and Omega-3 Trail"
- VitaminDCouncil.org: "Depression", "Multiple Sclerosis"