This article will summarize all of the must-know information about vitamin D nutrition for registered dietitians.
Dietitian Success Center’s membership includes access to vitamin & mineral supplement guides, a comprehensive yet simplified reference for finding the best supplements for your clients. You can quickly find information on recommending vitamin D supplements in DSC’s vitamin D supplement reference chart.
Written by Miranda Galati, RD
Reviewed by Olivia Farrow, RD, MHSc
Vitamin D Nutrition
Vitamin D is a fat-soluble micronutrient needed for survival (1, 2, 3).
The term “vitamin D” refers to vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) (4).
Vitamin D plays a role in bone health, muscle function, cognition, immunity and more (1).
Humans obtain most of their vitamin D through sunlight (1, 2, 3). The body produces vitamin D from cholesterol through exposure to ultraviolet radiation (UV) from the sun (5). This conversion starts in the skin and continues in the liver and kidneys, before being transported for use throughout the body (5). Vitamin D is also found in select food sources such as fatty fish, mushrooms and eggs, as well as supplements (2, 6).
Vitamin D – Role in the Body
Vitamin D is best known for helping the body regulate blood calcium levels to build and maintain strong bones and teeth (2, 1, 6). It also plays a role in cell growth, neuromuscular function, immunity and glucose metabolism (6).
The body of evidence on vitamin D nutrition is growing yet still highly contradictory (2, 4). Although its role in bone health is clear, more research is needed to understand exactly how vitamin D may impact different facets of health (2, 4). Early research shows that vitamin D may support:
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- COVID-19 due to its role in immunity (19)
Additional areas of research exploration include colorectal cancer, asthma, body fat, multiple sclerosis (MS), respiratory infection, and more (3).
Although this research is exciting, the extent of these relationships and whether supplementation is warranted remains unclear. Aside from bone health, no firm conclusions can be drawn regarding the vitamin D nutrition role in various health concerns.
Vitamin D Daily Requirements
Canadian and US health authorities have set the dietary reference intakes (DRIs) for vitamin D around 600IU for most adults (6,1).
Because the research landscape is so contradictory, the DRIs are set to optimize bone health specifically (6). The DRIs also assume that sun exposure is minimal (6).
Vitamin D Deficiency
Vitamin D deficiency is measured by serum concentrations of 25(OH)D. Deficiency causes blood calcium and phosphorous levels to decrease, which pulls calcium from the bones (6). This may result in rickets in children, and osteomalacia or osteoporosis in adults (6, 1).
Vitamin D deficiency can occur because of limited sun exposure or impaired absorption. This may be confounded by limited oral intake, but diet alone is unlikely to cause deficiency (20). Certain groups are more at risk of deficiency, including:
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- Breastfed infants because breastfeeding alone cannot provide adequate vitamin D and infants do not obtain adequate sun exposure (1).
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- People with dark skin because darker skin converts vitamin D less efficiently (1).
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- People residing in northern latitudes or with limited sun exposure (6) .
Other factors that may limit vitamin D synthesis in the skin include time of day, smog, sunscreen and heavy clothing (6). Data suggests that approximately 35% of American adults and 32% of Canadians are deficient or are at risk of vitamin D nutrition deficiency (4, 22).
Food Sources of Vitamin D
Vitamin D is naturally occurring in a limited number of foods including cod liver oil, fatty fish, mushrooms and eggs (2, 6).
Vitamin D can also be found in select fortified foods. In Canada, cow’s milk and margarine must be fortified with vitamin D (6). In the US, cow’s milk is required to be fortified with vitamin D (1). In both countries, goat’s milk, plant beverages, calcium-fortified orange juice and breakfast cereals are commonly fortified with vitamin D (1, 6).
It is difficult to achieve adequate vitamin D nutrition intake through diet alone (20, 4). This is because few foods naturally contain vitamin D and fortification is inconsistent and largely optional (20).
A complete list of food sources and their vitamin D content can be found in the table below.
Vitamin D Nutrition Content of Foods
| Food | Serving | Amount of vitamin D (IU) |
| Cod liver oil | 1 Tbsp | 1360 |
| Trout | 3 ounces, cooked | 645 |
| Salmon | 3 ounces, cooked | 570 |
| Mushrooms | ½ cup, white, raw | 366 |
| Milk, 2% milkfat | 1 cup | 120 |
| Soy, almond and oat milks, vitamin D fortified | 1 cup | 100-144 |
| Ready-to-eat cereal, fortified with vitamin D | 1 serving | 80 |
| Sardines | 2 sardines, canned in oil and drained | 46 |
| Egg | 1 large | 44 |
(2)
Recommendations to Increase Intake
Recommendations to increase vitamin D intake include:
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- Spend 10-15 minutes outside daily (23).
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- Consume vitamin D containing foods regularly such as fatty fish, cow’s milk and eggs (2).
Most people should first rely on sun exposure to meet vitamin D needs. Consuming vitamin D containing foods is a bonus but likely not adequate to achieve optimal serum levels. If adequate sun exposure cannot be achieved (or if someone falls into any other at-risk group), then supplementation may be considered (1, 2, 3).
Indications for Supplementation
Anyone who is unable to obtain adequate vitamin D or who is at risk of deficiency may consider vitamin D supplementation (20).
Research is being conducted to explore the role of vitamin D with fall risk, cardiovascular disease, blood lipids, immunity, depression, mental health, cancers, asthma, body composition, and more. However, it is unclear whether supplementation is warranted for treatment or prevention for these conditions.
DSC’s vitamin D supplement reference guide for dietitians can support you with recommending vitamin D supplements including choosing the best vegan vitamin d supplement for your plant-based clients.
Contraindications for Supplementation
Individuals taking the following medications should consult their physician before beginning a vitamin D supplement due to potential drug-nutrient interactions:
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- Weight loss drug Orlistat, which can impair vitamin D absorption (1).
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- Cholesterol-lowering statins such as atorvastatin, lovastatin, and simvastatin, whose effectiveness may be impacted by vitamin D supplementation (1).
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- Steroids such as prednisone, often used to treat autoimmune disorders, which can lower serum vitamin D levels (1).
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- Blood pressure medication Thiazide diuretics, which may raise blood calcium levels too high if supplementing with vitamin D (1).
The research on drug interactions and contraindications for vitamin D is still emerging (24). Some sources suggest that individuals with sarcoidosis, high blood phosphate, high blood calcium, high blood vitamin D, kidney stones or impared kidney function should take caution (25).
Many vitamin D3 supplements are made with animal products, however there are vegan vitamin d3 supplements available. These options are listed in detail in DSC’s vitamin D supplementation summary guide.
Take-Home Messages for Dietitians:
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- Vitamin D is a fat-soluble nutrient best obtained through sun exposure, although some foods contain vitamin D naturally or through fortification.
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- Supplementation may be considered for individuals who are unable to obtain adequate vitamin D through sun exposure or who have impaired absorption.
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- The research landscape is highly contradictory so supplementation guidelines are unclear for many patient populations.
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- Supplement doses of 1000-2000 IU per day is likely adequate for most people.
At DSC, we make it easier for dietitians and dietetic students to build expertise in topics including vitamin D supplements. Our vitamin and mineral supplement guides, nutrition courses, ready-to-use client handouts, and community can help you feel more confident.
Dietitian Success Center is THE professional development resource for dietitians and dietetic students. Our mission is to make it easier for dietitians and dietetic students to build expertise. We do this through evidence-based online nutrition courses, community, and ready-to-use client handouts. Plus – we give you the tools to start and grow your dietitian private practice!
References
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