Vitamin D Testing

Vitamin D Tests are available from Mary Carmody Nutrition in Cork and Carrigaline

What is Vitamin D and Vitamin D deficiency?

Vitamin D, a lipid-soluble vitamin and prohormone, is known to play an important role in bone metabolism through regulation of calcium and phosphate homeostasis. Although relatively few countries have nationally representative data available on the vitamin D status of their population, vitamin D deficiency is suspected to be a public health problem in many parts of the world.

In addition, vitamin D deficiency or insufficiency is common in pregnancy in some populations. The main risk factors of vitamin D deficiency are those that inhibit the body’s production of vitamin D in the skin, including dark pigmentation, too little exposure to sunlight, clothing that limits exposure of skin to sunlight, living in latitudes above 40° (both north and south), the season of the year, environmental pollution, use of sunscreen and ageing.

Vitamin D status is also affected by dietary consumption of vitamin D and factors affecting its absorption or metabolism, as well as obesity.

cork vitamin d test Mary Carmody Nutrition

Why test for a Vitamin D Deficiency

Vitamin D deficiency can be a serious problem. It doesn’t have obvious symptoms but increases susceptibility to more serious conditions. Data supports the view that maintaining Vitamin D levels protects against a wide range of diseases including viruses, cardiovascular disease, bone diseases such as osteoporosis, rickets and osteomalacia, autoimmune disease (such as multiple sclerosis, Hashimoto’s Thyroiditis and rheumatoid arthritis), strokes, nervous system disorders (such as Parkinson’s Disease) and type 1 & 2 diabetes. Depression and breast, prostate and colon cancer have also been linked to Vitamin D deficiency.

Causes of Vitamin D Deficiency

  • Deficient production
  • Increased metabolism
  • Decreased due to seasonal lack of exposure to sunlight
  • Anything that interferes with the penetration of solar ultraviolet radiation into the skin will diminish the cutaneous production of Vitamin D3 eg. clothing, sunscreen etc
  • Dietary intake is low
  • Decreased capacity of human skin to produce vitamin D in the elderly
  • Impaired absorption due to kidney or digestive diseases

Which foods contain Vitamin D

Only a few foods naturally contain Vitamin D therefore adequate levels are largely dependent on exposure to sunlight. The flesh of fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources. Small amounts of vitamin D are also found in beef liver, cheese, and egg yolks.  Vitamin D2 will also raise blood levels and can be found in sun-exposed mushrooms (including purchased mushrooms placed in sunlight) as well as seaweeds (e,g, kelp) and yeast products (reportedly even in some beers). While less desirable as sources, fortified processed foods such as breakfast cereals, yogurt, margarine contain added Vitamin D.

Vitamin D maintains levels of calcium and phosphate. These are needed for normal bone mineralisation, muscle contraction, nerve conduction & general cell function. More specifically 1, 25-dihydroxyvitamin D is a strong steroid hormone with a crucial role in calcium homeostasis, bone metabolism, cell growth and replication.

Vitamin D in Pregnancy

Vitamin D deficiency in pregnancy has been associated with an increased risk of pre-eclampsia, gestational diabetes mellitus, preterm birth, small-for-gestational age infants, impaired fetal skeletal formation causing infant rickets (softening of bones commonly leading to deformities and/or fractures) and reduced bone mass, as well as other tissue-specific conditions.
Immune dysfunction, placental implantation, angiogenesis (abnormal growth of new blood vessels from pre-existing vessels), excessive inflammation and hypertension in the mother have also been associated with vitamin D deficiency, although the underlying pathogenic mechanisms are not well understood.

Vitamin D status is most commonly assessed through measurement of serum 25-hydroxyvitamin D (25(OH) D or calcidiol) levels, which reflect the vitamin D produced cutaneously and that obtained from foods or supplements.

There is still controversy regarding adequate or optimal levels of serum 25(OH)D for overall health. The United States Institute of Medicine has recently defined levels of serum 25(OH)D greater than 50 nmol/L (or 20 ng/mL) as adequate for pregnant women; however, other investigators argue that optimal levels should be set higher (>75 nmol/L or 30 ng/mL).

Vitamin D supplementation in pregnancy improves maternal vitamin D status and may positively affect the availability of vitamin D to the fetus and the neonate. The fetus is dependent on the mother for acquiring vitamin D, and 25(OH)D readily crosses the human placenta.

The World Health Organization/Food and Agriculture Organization of the United Nations (WHO/FAO) recommended nutrient intake (RNI) for vitamin D in pregnant women is 5 μg (200 IU) per day (37).

Dietary sources of vitamin D include both food and dietary supplements. Vitamin D occurs naturally in oily fish such as salmon, mackerel and herring, cod liver oil, and egg yolk.




Risk Factors for Deficiency include

    • Vitamin D production in the skin depends on the incident angle of the sun and thus latitude, season and time of day. Consequently people with dark or covered skin and users of sunscreen, synthesise less vitamin D.
    • Sun exposure during the winter months at latitudes above approximately 33 degrees north or below 33 degrees south is insufficient for production of vitamin D3 in the skin. Ireland is above 40ºN.
    • People taking medication can significantly deplete vitamin D status e.g. steroids, metformin, anti-convulsants and medications that interfere with digestion/absorption such as proton pump inhibitors.
    • People who are obese( as vitamin D is deposited in body fat stores, making it less bio-available) and/or have a sedentary lifestyle(likely to have reduced sun exposure)
    • People with digestive impairments such as IBD, especially those who have had small bowel resections, or fat malabsorption disorders.
    • Pregnant and breastfeeding women
    • Babies( particularly exclusively breastfed) and young children under 5 years of age.
    • The elderly, due to reduced capacity to synthesise vitamin D in the skin when exposed to UVB radiation

Also did you know that studies have shown distinct demographic differences in rates of vitamin D insufficiency and deficiency with people with darker skins/skin tone.

What you can do now?

  1. Get tested
  2. When the sun shines, jump out into it, we should get at least 15 mins three times a week.
  3. Resistance exercise, [lifting weights in the gym, using your body weight in yoga] are useful for promoting bone growth.
  4. Eat more Oily fish like salmon, mackerel and herring [wild!]
  5. Eat good quality eggs
  6. Supplementation with a good quality Vitamin D3 supplement.

What is the optimal range on a blood test?
Optimal range is 50-100 ng/mL (125-250 nmol/L). Mary likes to see readings over 80ng/mL at the Vitamin D tests in her Cork clinics.

Having blood tests to measure the amount of vitamin D in your blood is the only way to know if you’re getting enough vitamin D or not.

Sample requirements & test turnaround

Mary Carmody perform Vitamin D tests in her clinic in Cork or on site with corporate clients.

The test involves a simple finger prick and after 15 mins your results will be ready,  include a consultation, your appointment  will last approx 1 hour. A follow up consultation and test is strongly recommended after 3 months.

Mary can also perform a more detailed test where your sample is sent to the lab. Mary will do this test for you at either clinic in Cork or Carrigaline and include a consultation for you lasting approx 1 hour and follow up with results after approx 2 weeks.