Vitamin D deficiency is considered a worldwide public health problem, in particular, because in most countries, large parts of the general population do not meet the dietary vitamin D requirements as recommended by nutritional vitamin D guidelines.
A 2020 Australian-based study showed 59.8% of the population to be insufficient. Arguably the rates are higher as this study classified deficiency as <75nmol/L and in most Australian labs the classification for deficiency is <50nmol/L.
In pregnancy, low levels of vitamin D have been associated with a higher risk of gestational diabetes mellitus (GDM) and in Australia it has now been reported that over 10% of women have GDM during their pregnancy.
So with one in ten pregnant women being diagnosed with GDM and with an alarmingly high rate of vitamin D deficiency shouldn't we be routinely testing?
According to the current Australian guidelines, universal screening and treatment of low vitamin D levels is not recommended as a result of the lack of evidence.
This however does not mean there isn't an association, rather the right paper has yet to be published to satisfy the requirements of the guidelines.
Here is what the existing studies are telling us about vitamin D and GDM
- A 2018 systemic review, following the examination of 87 observational studies and 25 randomised controlled trials involving over 58 000 subjects, found an 85% higher risk for gestational diabetes when vitamin D levels were low
- Several observational studies have found an association between low vitamin D level and increased risk of GDM
- Vitamin D has been shown to improve pancreatic exocrine function and insulin sensitivity in animal models
- Vitamin D deficiency in women with GDM is associated with an elevated risk of postpartum glucose intolerance
- Women who develop GDM have a risk of developing Type II diabetes by 5 years postpartum of 5-25% and a lifetime risk of approximately 60%
- Vitamin D levels were inversely correlated with fasting plasma glucose, fasting insulin level, and HgbA1c
Maternal and fetal impact of GDM
- The fetus has no insulin production <14 weeks and is exposed to high glucose levels from women with pre-pregnancy diabetes.
- In early pregnancy there is an increased risk of fetal congenital abnormalities, particularly cardiac and neural tube defects
- Later in pregnancy there is an increased risk of preeclampsia, UTI's, macrosomia (large birth weight babies) and preterm labour
- Increased chance of c-section, difficult birth
- Post birth lower breastfeeding rates, higher rate of depressive symptoms, increased rate of urinary incontinence,
- Life long increased risk of type 2 diabetes, increased risk of childhood obesity, insulin resistance and childhood obesity
- Increased risk of stillbirth, leading to a generally accepted policy of induction of labour at around 38-40 weeks
What to know about Vitamin D testing & supplementation
- Vitamin D testing can be elected at a cost to the patient, usually around $50-75
- Testing is only required every 12 months in women of childbearing age
- Ideal levels in preconception and pregnancy are between 100-200nmol/L
- Vitamin D intake from supplement/food/sun sources above 600IU/day should be taken under the guidance of a health care professional
- If vitamin D deficiency is detected, 1000UI - 4000UI/day vitamin D is considered safe in pregnancy
- Most high-quality pregnancy multivitamins will contain between 500-1000IU vitamin D
- Vitamin D3 (cholecalciferol) is the preferred form of vitamin D
- Vitamin D is found in animal foods such as fish, meat, organ meats (not recommended in pregnancy), dairy, eggs
- 20 minutes in mid-morning summer sun and midday winter sun daily will give you approx 1000IU vitamin D, depending however on genetic variability.
- If you are of childbearing age ask your GP when was your last vitamin D testing, if >12 months retest
- If you have a family history of GDM or a current history of diabetes or insulin resistance request vitamin D testing with your doctor (you may need to pay)
- Preventative supplementation can reduce the incidence and severity of GDM and its lifelong impact
- Supplementation should always be under the guidance of a health care professional
- Preconception/pregnancy vitamin D levels ideally should be between 100-200nmol/L.
Jennifer Ward, Adv dip Nat, BCom Econ, competing Masters Repro Med
Jennifer is a qualified naturopath with a focus on fertility, pregnancy, hormonal imbalances.
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