Vitamin D
    In children 

Vitamin D (cholecalciferol)

·     Vitamin D is a fat soluble vitamin that is found in food and can also be made in your body after exposure to ultraviolet (UV) rays from the sun.

·     Vitamin D exists in several forms, each with a different level   of activity.        

·     Calciferol is the most active form of vitamin D.

·     Other forms are relatively inactive in the body.

·     The two major forms are  :
   Vit. D2 (ergocalciferol ) derived from fungal and plant sources .

·     Vit. D3 (cholecalciferol ) is derived from animal sources and is made in the skin when 7;-dehydrocholesterol reacts with UVB   .

     sources Vitamin D

     ·     Fortified foods represent the major dietary sources  of vitamin D, as very                   few foods naturally contain significant amounts of vitamin D.

          In the 1930s, rickets was a major public health problem in the (U.S.).

        A milk fortification program was implemented to combat rickets, and it nearly eliminated this disorder in the U.S.

       About 98% to 99% of the milk supply in the U.S. is fortified with 10 micg (equal to 400 International Units or IU) of vitamin D per quart.

        One cup of vitamin D fortified milk supplies one-half of the recommended daily intake for adults between the ages of 19 and 50.

Natural sources of vitamin D  

·    Fatty fish, such as salmon, tuna , sardines ,are natural sources of vitamin D. 

·    Fish liver oils, such as cod liver oil ,1tab (15 mL) provides 1,360 IU

·    Mushrooms : provide over 2700 IU per serving (approx. 1/2 cup) of vitamin D2, if exposed to just 5 minutes of UV light after being harvested this is one of a few natural sources of vitamin D for vegans.

 ·    One whole egg 20 IU

What is the recommended intake for vitamin D?   

Three important types of reference values included in the DRIs (Dietary Reference Intakes)   :

The Recommended Dietary Allowances (RDA)

 recommends the average daily intake that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each age and gender group.

   Adequate Intakes (AI)

     is set when there is insufficient scientific data available to establish a RDA. AIs meet or exceed the amount needed to maintain a nutritional state of adequacy in nearly all members of a specific age and gender group.

The Tolerable Upper Intake Level  (UL ) :

     is the maximum daily intake unlikely to result in adverse health effects

The recommended intake for vitamin D

·     The recommended intake is listed as an Adequate Intake (AI), which represents the daily vitamin D intake that should maintain bone health and normal calcium metabolism in healthy people.

Prevention of rickets :

   exposure to ultraviolate light or by vit D orally (400 iu daily ).

Treatment of rickets :

 50-150micg vit.3 or 0.5-2micg 1,25 dihydroxcholecalcifero (2- wks ).

    A single dose of 15,000micg of vit D (without further therapy for several months )

    The biological activity of 1 μg vitamin D is equal to 40 IUs

The recommended intake for vitamin D

When can vitamin D deficiency occur ?

Nutrient deficiencies are usually the result of dietary inadequacy, impaired absorption and utilization, increased requirement, or increased excretion (loss).

·    A deficiency of vitamin D can occur

   1) when usual intake is below recommended levels .

   2) when there is limited exposure to sunlight

   3) when the kidney cannot convert vitamin D to its active hormone form.

   4) when someone cannot adequately absorb vitamin D from the digestive tract .

When can vitamin D deficiency occur ?

·    Prolonged exclusive breastfeeding without vitamin D supplementation is one of the most significant causes of the rickets( especially those with dark skin, and those living in inner city areas ).

·    Rickets is more prevalent among immigrants from Asia, Africa, and Middle Eastern countries for a variety of reasons , vit D deficiency has been associated with iron deficiency, (question whether or not iron deficiency may impair vitamin D metabolism) .

Diseases caused by deficiency

·    Rickets : failure to mineralize growing bone, leading to impaired growth (rickets dwarfism ), and deformity  of the long bones ( bow legs , small deformity pelvic ) delay teething ( caries ), delay stand and walk (lack of muscle tone ). C/signs : craniotabes ,forming prominence (bosses ) ,thickening of wrist and ankle , rachitic rosary (chest ),delayed closures A.F ,

·    Osteomalacia   :

a bone-thinning disorder that occurs exclusively in adults and is characterised by proximal muscle weakness and bone fragility.

  Diseases caused by deficiency.

          Osteoporosis : 

            a condition characterized by reduced bone mineral density and increased                  bone fragility.

·    Vitamin D malnutrition may also be linked to an increased   susceptibility to several chronic diseases such as: High blood pressure  , T B , Cancer , periodental disease , multiple sclerosis , chronic pain , depression , schizophrenia , and several autoimmune diseases including DM type 1 .                  

 Who may need extra vitamin D to prevent a deficiency?

1) Infants who are exclusively breastfed
(breast milk provides approximately 25 IU vitamin D/L ) .

·     The American Academy of Pediatrics recommends a daily supplement of 200 IU vitamin D for breastfed infants beginning within the first 2 months of life unless they are weaned to receive at least 500 ml per day of vitamin D-fortified formula .

·     The minimal level of fortification (milk formula ) required is 40 IU vitamin D per 100 calories of formula and the maximum level of vitamin D fortification allowed is 100 IU per 100 calories of formula .

Who may need extra vitamin D to prevent a deficiency? 

2) Older adults.

    As people age, skin cannot synthesize vitamin D as efficiently and the kidney is less able to convert vitamin D to its active hormone form .

 3) Persons with limited sun exposure.

 4)  Persons with greater skin melanin content.

 5) Persons with fat malabsorption .

   vitamin D requires some dietary fat for absorption. Pancreatic enzyme deficiency , Crohn's Disease , Cystic Fibrosis , Celiac Disease , Liver disease Surgical removal of part or all of the stomach or intestines can impair digestion and absorption of many nutrients.

Other role of vit .D

·     Vitamin D and cancer:
evidence suggests that vitamin D may be protective against some cancers. Epidemiologic studies suggest that a higher dietary intake of calcium and vitamin D, and/or sunlight-induced vitamin D synthesis, correlates with lower incidence of cancer.

·     Role in coronary disease prevention

    Research indicates that vitamin D plays a role in preventing coronary disease. As with cancer incidence, the same qualitative inverse correlations exist between coronary disease incidence and serum vitamin D levels.

 Vitamin D and steroids: Corticosteroid medications such as prednisone have potential side effects, including decreased calcium absorption may also impair vitamin D metabolism.

Vitamin D and caffeine: High caffeine intake may accelerate bone loss.

             Caffeine may inhibit vitamin D receptors, thus limiting absorption of vitamin D and decreasing bone mineral density. A study found that elderly postmenopausal women who consumed more than 300 milligrams per day of caffeine lost more bone in the spine than women who consumed less than 300 milligrams per day .

What are the health risks of too much vitamin D?

Vitamin D toxicity can cause nausea, 

vomiting, poor apetite, constipation, weakness, and weight loss.

It can also raise blood levels of calcium causing confusion. heart rhythm abnormalities. Calcinosis, the deposition of calcium and phosphate in the body's soft tissues such as the kidney,

Sun exposure ,Diet are unlikely to cause vitamin D toxicity, unless large amounts of cod liver oil are consumed.

 

Vitamin D toxicity is much more likely to occur from high intakes of vitamin D in supplements.

Vitamin D toxicity( hypervitaminosis D)

over 500 micg /d for weeks = toxicity

Tolerable Upper Intake Level (UL) of vitamin D for children and adults is 50 micrograms/day (2,000 IU/day).

 

      Long term intakes above the UL increase the risk of adverse health effects.

 In adults, sustained intake of 2500 micrograms/day (100,000 IU) can produce toxicity within a few months .

 For infants (birth to 12 months) the tolerable UL is set at 25 micrograms/day (1000 IU/day), and vitamin D concentrations of 1000 micrograms/day (40,000 IU) in infants has been shown to produce toxicity within 1 to 4 months.

Vitamin D toxicity .

·    Serum levels of calcidiol (25-hydroxy-vitamin D) are typically used to diagnose vitamin D overdose.

·    Vitamin D toxicity is treated by discontinuing vitamin D supplementation, and restricting calcium intake. If the toxicity is severe blood calcium levels can be further reduced with corticosteroids or bisphosphonates. In some cases kidney damage may be irreversible .