Vitamin D: Recommendations and Dietary Sources

Abstract

In this article, we describe:

  • the major purposes of this specific nutrient in the human body, 
  • its experimentally confirmed health uses, 
  • conventional ways to estimate nutrient status,
  • nutrient’s toxicities and deficiencies,
  • experimentally confirmed and approved levels of the nutrient intake for different demographics,
  • dietary sources of the nutrient.

Introduction

Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation.

Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis.

Vitamin D has some other roles in the body. Many cells have vitamin D receptors.

Serum concentration of 25-hydroxyvitamin D [25(OH)D], also known as calcidiol, is the best indicator of vitamin D status. 25(OH)D functions as a biomarker of exposure, but it is not clear to what extent 25(OH)D levels also serve as a biomarker of effect (i.e., relating to health status or outcomes). Serum 25(OH)D levels do not indicate the amount of vitamin D stored in body tissues.

Based on its review of data of vitamin D needs, a committee of the Institute of Medicine concluded that persons are at risk of vitamin D deficiency at serum 25(OH)D concentrations <30 nmol/L (<12 ng/mL). Some are potentially at risk for inadequacy at levels ranging from 30–50 nmol/L (12–20 ng/mL). Practically all people are sufficient at levels ≥50 nmol/L (≥20 ng/mL); the committee stated that 50 nmol/L is the serum 25(OH)D level that covers the needs of 97.5% of the population. Serum concentrations >125 nmol/L (>50 ng/mL) are associated with potential adverse effects.

Obtaining sufficient vitamin D from natural food sources alone is difficult. For many people, consuming vitamin D-fortified foods and, arguably, being exposed to some sunlight are essential for maintaining a healthy vitamin D status. In some groups, dietary supplements might be required to meet the daily need for vitamin D. These groups include breastfed infants; older adults; people with limited sun exposure; individuals with darker skin; people with inflammatory bowel disease and other conditions causing fat malabsorption; people who are obese or who have undergone gastric bypass surgery.

Vitamin D had been shown to provide benefits for osteoporosis. Strong biological and mechanistic bases indicate that vitamin D plays a role in the prevention of colon, prostate, and breast cancers. Emerging epidemiologic data suggest that vitamin D may have a protective effect against colon cancer, but the data are not as strong for a protective effect against prostate and breast cancer, and are variable for cancers at other sites. However, one study of Finnish smokers, for example, found that subjects in the highest quintile of baseline vitamin D status had a threefold higher risk of developing pancreatic cancer.

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Vitamin D toxicity can cause non-specific symptoms such as anorexia, weight loss, polyuria, and heart arrhythmias, but also, it can raise blood levels of calcium which leads to vascular and tissue calcification, with subsequent damage to the heart, blood vessels, and kidneys.

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Recommended Dietary Allowances (RDAs) for Vitamin D

AgeMaleFemalePregnancyLactation
0–12 months*400 IU
(10 mcg)
400 IU
(10 mcg)
1–13 years600 IU
(15 mcg)
600 IU
(15 mcg)
14–18 years600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
19–50 years600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
51–70 years600 IU
(15 mcg)
600 IU
(15 mcg)
>70 years800 IU
(20 mcg)
800 IU
(20 mcg)

* Adequate Intake (AI). Upper tolerable limit for 9 years and older is 4,000 IU
(100 mcg).

Food Sources of Vitamin D

Very few foods in nature contain vitamin D. The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources. Small amounts of vitamin D are found in beef liver, cheese, and egg yolks. Vitamin D in these foods is primarily in the form of vitamin D3 and its metabolite 25(OH)D3. Some mushrooms provide vitamin D2 in variable amounts. Mushrooms with enhanced levels of vitamin D2 from being exposed to ultraviolet light under controlled conditions are also available.

In Canada, milk is fortified by law with 35–40 IU/100 mL, as is margarine at ≥530 IU/100 g. In the 1930s, a milk fortification program was implemented in the United States to combat rickets, then a major public health problem. Other dairy products made from milk, such as cheese and ice cream, are generally not fortified. Ready-to-eat breakfast cereals often contain added vitamin D, as do some brands of orange juice, yogurt, margarine and other food products. Plant milk alternatives (such as beverages made from soy, almond, or oats) are often fortified with vitamin D to the amount found in fortified cow’s milk (about 100 IU/cup); the Nutrition Facts label will list the actual amount.

Both the United States and Canada mandate the fortification of infant formula with vitamin D: 40–100 IU/100 kcal in the United States and 40–80 IU/100 kcal in Canada.

Selected Food Sources of Vitamin D

FoodMicrograms (mcg) per servingIUs* per servingPercent DV**
Cod liver oil, 1 tablespoon34.01,360170
Cooked rainbow trout, farmed, 3 ounces16.264581
Cooked sockeye salmon (), cooked, 3 ounces14.257071
Mushrooms, white, raw, sliced, exposed to UV light, 1/2 cup9.236646
Milk, 2% milkfat, vitamin D fortified, 1 cup2.912015
Sardines (Atlantic), canned in oil, drained, 2 sardines1.2466
Soy, almond, and oat milks, vitamin D fortified, various brands, 1 cup2.5−3.6100−14413−18
Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 1 serving2.08010
Egg, 1 large, scrambled (vitamin D is in the yolk)1.1446
Liver, beef, braised, 3 ounces1.0425
Tuna fish (light), canned in water, drained, 3 ounces1.0405
Cheese, cheddar, 1 ounce0.3122
Mushrooms, portabella, raw, diced, 1/2 cup0.141
Chicken breast, roasted, 3 ounces0.141
Beef, ground, 90% lean, broiled, 3 ounces01.70
Broccoli, raw, chopped, 1/2 cup000
Carrots, raw, chopped, 1/2 cup000
Almonds, dry roasted, 1 ounce000
Apple, large000
Banana, large000
Rice, brown, long-grain, cooked, 1 cup000
Whole wheat bread, 1 slice000
Lentils, boiled, 1/2 cup000
Sunflower seeds, roasted, 1/2 cup000
Edamame, shelled, cooked, 1/2 cup000

* IUs = International Units.
** DV = Daily Value. The DV for vitamin D used above is 20 mcg (800 IU) for adults and children age 4 years and older. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

References

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