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Vitamin D – Very important in human body


Usually results from inadequate dietary intake. Also, form insufficient ultra violet irradiation of the skin (not enough sunshine), or from impaired conversion to the active forms. Deficiency occurs with little or no fat in the diet, or little or no exposure to sunlight. So, if you are always indoors and/or eat a very low-fat diet, you are at high at risk and should get tested and incorporate dietary sources and supplement as recommended by your dietitian.

Vitamin Forms

1,25-(OH)2: Calcitriol: Active Form and comes from animal products. D2: Ergocalciferol: Major synthetic form and comes from plants, most common form in supplements.



Meta-analysis of many published papers suggests that an optimal serum concentration of 25(OH) vitamin D is 75 nmol/L and above; dietary intakes to achieve this serum level range from 700-10000 IU (17.5-25 ug)/d. One IU =0.025 ug vitamin D3, or 40 IU/ug; activity of 25(OH) vitamin D is 60 IU/ug and 1,25(OH2) vitamin D is 200 IU/ug.  

Importance to Your Health

Bone Health

Main role is the maintenance and metabolism of calcium and phosphorus, mainly by increasing blood calcium levels; normal individuals absorb about 30% of dietary calcium whereas vitamin D deficient persons absorb 10-15% of dietary calcium. Bone lesions have long been known to occur with vitamin D deficiency.

Kidneys & Thyroid

Vitamin D is activated in the kidneys. Without the activated vitamin D to control calcium and phosphorous levels in the blood, the body will produce more parathyroid hormone (PTH) which works to cause the body’s bones and organs to release more calcium into the blood to keep normal levels. This means your bones will become weaker and brittle. The PTH hormone is released by the parathyroid glands located in the neck near the thyroid glands.


Vitamin D is absorbed from the intestine and involves calcium exchange and is influenced by hormonal changes of estrogen, prolactin, glucocorticoids and aging.

Immune System

Vitamin D helps keep you from getting sick. Deficiency is associated with autoimmune disorders and sickly nature sue to its within the immune system. In short, your immune system is the body’s defense against infectious organisms and other invaders. Vitamin D plays a role in the immune response which attacks these organisms and substances that invade your body and cause disease.


In vivo experiments show suppression of growth of cancer cells in culture as well as a reduction of colon cancer occurrence.  Recent experiments show that high dietary intakes of vitamin D are associated with lower rates of colon, breast, ovarian, and prostate and pancreatic cancer.  Those taking the most supplemental vitamin D had the lowest rates of cancer.

Factors Influencing Needs

Age:  Infants, children, and adolescents have higher needs due to bone formation and mineralization. Women may have higher needs to offset osteoporosis due to lower amount of bone mineralization of women.




Except during the summer months, the skin makes little if any vitamin D from the sun at latitudes above or below 37 degrees latitude (red line).  The minimum requirement of vitamin D can be met by most people during spring, summer and fall by adequate exposure to sunlight; amount synthesized dependent on latitude of exposure and season of year; worst in winter. A recent study shows>40% healthy men in Boston had levels of serum vitamin D in the insufficient range by the end of winter.


High caffeine intake (> 300mg/d or >18 oz brewed coffee) accelerate bone loss at the spine of elderly post-menopausal women. That is just 2 cups of coffee or one very strong cup of coffee per day if counting caffeine!


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A recent study showed that about 42% of African American women and only 4% of Caucasian women had serum levels of 25(OH) below normal levels. African Americans require 5 times the sun exposure of Caucasians to elicit the same increase in plasma vitamin D concentration.

Dietary Sources

Best: oily fish (salmon, mackerel, sardines) and fish liver oils; fortified milk – this is responsible for prevention of rickets: fortified cow milk contains 10 ug/L, which is the greatest source of the vitamin for children, other good sources include eggs, butter and fortified margarine, orange juices, and some breakfast cereals.

How to Test

The best way to find out if you are deficient is to take a serum level test for 25(OH). Standard clinical assessments test for serum concentrations of 25(OH) vitamin D. Normal concentrations of 25(OH) vitamin D are 11 to 60 ug/L (27.5 – 150 nmol/L) concentrations between 25 and 50 ug/L are considered as vitamin D insufficient and concentrations less than 25 nmol/L are used as a regular cut-off for regular insufficiency. Do not test for 1,25(OH2) for vitamin D deficiency because this one is dependent on parathyroid hormone and this reading is not accurate for vitamin D status.

Excessive Intake – Toxicity

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Since Vitamin D is stored in the fat tissue of your body, it can accumulate in the fatty tissue and at high levels be toxic to your health. Young persons are the most susceptible. ADULTS: Do not exceed more than 10,000 IU or 250 ug/day. CHILDREN: Do not exceed more than 45 ug/d or 1,800 IU/d).

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