Iodine in pregnancy and lactation
Iodine is a naturally occurring mineral that our bodies need for regulation of our metabolism. In pregnancy, the fetus relies on the mother to supply an adequate amount of iodine and, after birth, infants rely on breastmilk (or formula) to supply iodine.
The thyroid gland (a gland present in our necks; when it is enlarged it is called a ‘goitre’) requires iodine to produce thyroid hormone essential for regulation of metabolism. A deficiency of iodine or thyroid hormone in adults can result in fatigue, memory loss, dry hair and skin, slow reflexes and weight gain. In the developing fetus and in babies iodine deficiency can affect normal brain development resulting in lowered IQ, intellectual disability and diminished growth. Therefore, it is essential that pregnant and lactating women have an adequate daily intake of iodine.
So where do we get iodine from? Iodine content in food varies but is generally higher in seafood and dairy food, including eggs. A balanced diet will supply adequate iodine in most cases, but as pregnant and lactating women have a greater requirement, dietary sources may not be enough. Australia is now considered an iodine deficient country. This has occurred due to 2 main reasons: firstly, our increased consumption of processed foods has increased our salt intake but the food industry does not usually use iodised salt. Secondly, in the past, milk was stored in containers that were cleaned and sanitized using iodine containing disinfectants. The iodine in these cleaning agents leached into the milk. The iodine was theoretically a contaminant of the milk but actually was beneficial in supplying a significant amount of our daily iodine requirement. Now the dairy industry uses mainly chlorine based disinfectants so the iodine levels in milk have dropped.
How much do we need? Most adults require 150 mcg (MICROGRAMS) per day but pregnant women need 220-250mcg and lactating women need 270mcg per day. Fetuses will extract about 15mcg per day up to about 90mcg by term. Much of this transfer occurs in first trimester when maternal thyroid hormone production increases by about 50%. So as soon as a woman is pregnant her requirement for iodine increases significantly. Allowing an extra 100mcg daily from conception will cover this increased need.
Australia has a programme to assist people to get enough iodine into their diet. Bread is now fortified with iodine. This is mandatory. The only bread that escapes this law is ‘organic’ bread. This fortification programme alone increases the average daily intake by 50mcg daily. Also, salt is a major potential source of iodine. However, salt must be ‘iodised’. Natural sea salt does NOT contain much iodine. Therefore, using ‘iodised’ salt will add to our daily intake. Most Australian households have reduced the amount of salt used in cooking, but when they do it is often non-iodised salt. Simply replacing salt used in cooking or added at the table with iodised salt (it is on the salt packet – it has to be by law) will increase daily intake of iodine. Iodised salt contains approximately 200mcg per teaspoon (6g).
In addition, to ensuring adequate dietary intake (food or iodised salt) pregnant women may also need a supplement. Most multivitamins now contain iodine as an ingredient. It is usually recommended that a vitamin supplement contain between 150 to 250 mcg of iodine. There is no evidence that supplementation above 500mcg daily is beneficial. The maximum dose of additional supplementation is about 750mcg. Although only a small amount of iodine is stored in the thyroid gland and extra iodine is excreted by the kidneys, there is no safety data on taking more than 1000mcg daily so it is recommended to keep both dietary and supplement intake below 1000mcg daily.
Are there any circumstances where extra iodine supplementation should be avoided? Yes. In people with pre-existing thyroid disease having too much additional iodine may interfere with their thyroid function or medication requirements. Any iodine supplementation should only be taken under medical supervision. Also, some people are ‘iodine sensitive’.
What supplements can I take? As stated, most multivitamins contain iodine now. Check yours. Take into account the amount of iodine in the tablet and HOW MANY tablets you take daily. Additional supplementation can be taken in the form of iodine drops, iodine tablets (eg ‘Neurotabs’), tablet combinations (eg Blackmores I-Folic: iodine PLUS folic acid) etc. It is best to AVOID kelp supplements. Although kelp is a very good source of iodine (hence why sushi has a high iodine content because of the seaweed wrap), the amount of iodine in each kelp supplement can be variable AND the kelp supplement may contain higher doses of mercury.
How reliable is the test itself? The best test we have is a urinary iodine level. This measures the urinary excretion of iodine (hence a reflection on how much extra you have which is being excreted). If you are only excreting a small amount of iodine (less than 100mcg per litre of urine) this indicates that you are not getting enough iodine in your diet. Australian data indicates that the average urinary excretion of iodine in women is about 80mcg per litre and the average daily intake is about 130mcg per litre. This is well below the recommended intake. Ideally women should have a dietary intake of at least 220 mcg daily. Adequate dietary intake should result in urinary excretion levels above 100mcg and ideally above 150mcg per litre.
So what is my advice to you?
Be aware that I ROUTINELY test at 10 and 28 weeks. This is over and above the antenatal testing recommendation. I do so because my patients are extra special people who deserve extra intelligent children! My hope is they have all those extra IQ points to become doctors and don’t have to become lawyers (ha ha – sorry – no offence to all those lawyer patients of mine….)*
If I contact you after your 10 week bloods to advise additional iodine supplementation DON’T PANIC! You have not broken your baby! Tiny fetuses need very little iodine to begin with and will take what they need from you. If I advise a supplement I will PRESUME you are already on a multivitamin, so I will be recommending supplementation with an iodine supplement ON TOP OF the multivitamin.
If I contact you after your 28 week bloods to advise additional iodine supplementation DON’T PANIC! You have not broken your baby!!! If your initial result was normal and you are continuing to take your multivitamin then tweaking things at 30 weeks will just keep things well in normal range.
- make sure your multivitamin contains some iodine.
- Make sure I am aware of which supplement you are taking (you should have noted this down at your first visit when you filled in the medical questionnaire).
- Make sure I am aware if you have specific dietary restrictions (eg if you don’t eat seafood or dairy) that may result in low dietary iodine intake (once again this information is requested on the questionnaire).
- If I advise extra iodine supplementation then take an extra supplement such as Blackmores I-folic 1 daily or Neurotabs 1 daily (others are OK – speak to your pharmacist). There is no need to contact me before your next appointment. I will discuss the result with you at your next appointment and if you are taking another type of supplement I will check this with you.
- See the foodstandards.gov.au website for a list of foods and their iodine content to help you determine any dietary changes you should make.
- Do not start taking excessive amounts of iodine. This may have detrimental effects on the fetal thyroid gland. Just add the supplement that I have advised.
- If you have an underlying thyroid condition speak to me about your individual situation.
*FYI my son is doing law this year at university…if only I had taken more iodine during his pregnancy ;-).