Medically reviewed by Dr. Jeffrey Gladd, MD – Written by Laura Dan, BSc, NDTR
Vitamin D is an essential vitamin responsible for numerous body functions, ranging from supporting bone health to regulating the immune system. Unlike other vitamins, vitamin D functions as a hormone, meaning that it serves as a messenger, controlling and coordinating activities throughout the body. (4)
Vitamin D can be obtained from some foods, but the body can also create its own. Often called the “sunshine vitamin”, vitamin D is synthesized by the body when invisible UVB rays from the sun are absorbed by the skin. (22) Vitamin D may also be obtained through supplementation if food intake and sun exposure do not provide enough.
Vitamin D benefits
Outlined below are some of the health benefits of vitamin D.
Promotes healthy bones
Vitamin D is essential for maintaining strong, healthy bones. Bone mass is determined by a number of factors, including genetics, physical activity, and nutrition. By age 40, bone mass begins to decline, increasing our risk of fractures and osteoporosis, a condition characterized by low bone mass. (16)
Calcium, a mineral that helps build and maintain strong bones, requires vitamin D for proper absorption. Vitamin D helps the body absorb calcium and maintain adequate calcium in the blood, which promotes bone mineralization. (31) If vitamin D levels are not sufficient, calcium is released from the bones to help maintain blood calcium levels, contributing to soft, brittle bones. (16)
Research suggests that supplementing with vitamin D may increase bone density, resulting in a decreased risk of osteoporosis and fracture. (10)
Boosts immune health
The immune system, the body system responsible for defending the body from foreign invaders, is influenced by vitamin D status. Low levels of vitamin D are associated with increased susceptibility to infection. (1)
Research has also identified a link between poor vitamin D status and multiple autoimmune diseases, including lupus, multiple sclerosis (MS), and rheumatoid arthritis (RA). Deficiency is common in individuals with autoimmune disease, however, improving vitamin D status, though supplementation, diet, and sun exposure, may have protective effects against autoimmune disease. (17)(36)
Several studies have found a correlation between optimal vitamin D levels and a decreased risk of upper respiratory tract infections, such as the common cold. (19)(28) It’s believed that this protective effect is the result of an increased expression of anti-microbial peptides in the lungs. (37)
May support healthy cardiovascular health
Vitamin D deficiency is a known risk factor for cardiovascular disease. While existing research is inconclusive, there is some evidence to suggest that supplementing with vitamin D may support heart health by lowering the risk of cardiovascular disease. (14)
Supplementing with vitamin D and calcium together may decrease risk of heart failure by 25 to 37%. (7)(8) Furthermore, sufficient vitamin D status may reduce elevated levels of parathyroid hormone (PTH), a hormone that regulates calcium in the blood. When excess PTH is secreted, risk of hypertension and heart failure increases. (3)(18)(38)
One study found that vitamin D supplementation may improve blood flow. (12) Another study of overweight adults with vitamin D deficiency investigated the effects of vitamin D supplementation on high blood pressure. After six months of supplementation, blood pressure significantly improved. (11)
May delay age-related cognitive decline
Age-related cognitive decline may be associated with vitamin D deficiency. Vitamin D receptors are found throughout the brain and research has shown that vitamin D may have neuroprotective effects, including reducing beta-amyloid plaques, a protein buildup that contributes to the development of Alzheimer’s disease. (30)
Some research suggests that supplementing with high doses of vitamin D may improve visual memory, particularly among individuals with vitamin D insufficiency. (25) While human studies are limited, one animal study showed that vitamin D supplementation improved age-related cognitive decline. (2)
How much vitamin D do you need?
The Food and Nutrition Board (FNB) sets intake reference values for various nutrients, including vitamin D. The established recommended dietary allowance (RDA) represents a daily intake of vitamin D that is sufficient to maintain bone health and normal calcium metabolism in healthy people.
Also established is the tolerable upper intake level (UL), which represents the maximum daily amount of a nutrient that is unlikely to cause adverse effects. Since vitamin D is stored in fat cells, excess amounts can build up to dangerous levels, causing high blood calcium and damage to the heart, blood vessels, and kidneys. (24)
The table below outlines the recommended daily intake for vitamin D in International units (IU) and micrograms (mcg), as well as the tolerable upper intake level, for different age groups. (24)
Recommended dietary allowances (RDAs) and tolerable upper intake level (UL) for vitamin D
Vitamin D deficiency
Vitamin D deficiency is very common, affecting approximately 41% of the population. (9) Low levels of vitamin D can have serious consequences and are associated with several health concerns, including diabetes, cancer, osteoporosis, and high blood pressure. (33)
Certain populations are at increased risk of developing a vitamin D deficiency, including older adults, those who live in northern regions of the world, breastfed infants (often a result of low vitamin D status in the mother), individuals with darker skin, people with a BMI ≥30, and individuals with certain chronic conditions affecting fat absorption (e.g., celiac disease and ulcerative colitis). (9)(20)(24)(32)
Vitamin D deficiency symptoms
Vitamin D deficiency may manifest itself in any of the following ways:
- Bone pain
- Chronic fatigue
- Muscle pain
- Weakness (15)
Sources of vitamin D
There are three key sources of vitamin D – sunlight, dietary sources, and supplements. (22)
Sunlight is a reliable source of vitamin D. When the UVB rays from the sun (the same rays that cause sunburn) come into contact with our skin, cholesterol in skin cells reacts by converting these rays into vitamin D. The success of this reaction depends on the amount of skin exposed to sunlight, as well as the amount of melanin in the skin. Melanin is the pigment that determines the color of our skin, hair, and eyes. The more melanin your skin contains, the darker your skin, resulting in fewer amounts of UVB rays absorbed by the skin. (23)
How much sun exposure is enough?
Spending approximately five to 30 minutes outdoors, twice per week, between the hours of 10 a.m. and 3 p.m. typically provides enough UVB to meet vitamin D needs. The face, arms, legs, or back, without sunscreen, should be exposed to the sun during this time. It’s important to note that sun exposure can increase the risk of skin cancer, so only spend short periods of time in the sun without protection. (21)
Vitamin D is naturally found in a limited number of foods, as well as in some vitamin D-fortified products. The list below outlines the most common food sources.
Natural food sources of vitamin D include:
- Beef liver
- Egg yolk
- Fatty fish (e.g., mackerel, salmon, and tuna)
- Some mushrooms (e.g., chanterelle, maitake, and UV-treated portabella) (13)(26)
Foods fortified with vitamin D often include:
- Breakfast cereals
- Dairy products (e.g., milk and yogurt)
- Non-dairy milk (e.g., soy and almond milk)
- Orange juice (24)
Did you know?
Since vitamin D is a fat-soluble vitamin, pairing vitamin D-rich foods or supplements with high-fat foods, such as avocados or nuts, can significantly increase absorption. (5)
People who spend limited time in the sun, don’t consume enough vitamin D-containing foods, or have low blood levels of vitamin D may benefit from a vitamin D supplement. (27) Vitamin D supplements are typically available in various forms, including capsules, chewable tablets, and drops. Talk to your healthcare practitioner, who can help determine if supplementation is right for you.
The bottom line
Vitamin D deficiency is common, however, it’s feasible to get enough through adequate sun exposure and intake of vitamin D-rich foods. If you are at risk for a vitamin D deficiency, consult your integrative healthcare practitioner for testing and specific recommendations.