The conventional view is that obesity is the result of eating too much and/or not being active enough. I don’t quite subscribe to this view myself, as I see body weight as the result of a complex interplay between a variety of factors including the form calories come in the diet and hormonal factors. One key hormone here is insulin – the chief hormone responsible for the accumulation of fat in the fat cells. Get insulin levels down and you have a pretty decent chance of losing weight.
Other key hormones that play a part in body weight maintenance include those hormones secreted by the thyroid gland. The most plentiful thyroid hormone is thyroxine (also known as T4). Thyroxine, essentially, stimulates the metabolism. Some of it, in health, is converted into a related hormone known as lio-thyronine (T3) that is more metabolically active. Should the body be deficient in thyroid hormone and/or the tissues be resistant to thyroid hormone (this latter idea I controversial) then ‘hypothyroidism’ (low thyroid function) is the result.
Hypothyroidism can bring with it many different signs and symptoms, but some of the more common include weight gain, fatigue, low mood/depression, dry skin, dry hair, constipation, sensitivity to cold and cold extremities. I’ve found excess weight in individuals with low thyroid function often to be quite resistant to eating right. Many individuals with low thyroid function feel as though their weight is ‘stuck’ somehow.
I was thinking about this today while reading this health story on the BBC website which informs us that the majority (almost 70 per cent) of teenage girls in the UK are deficient in the nutrient iodine. The relevance of this to thyroid function is that iodine is a critical nutrient for proper functioning of the thyroid and production of thyroid hormone. Iodine deficiency is well known to cause enlargement of the thyroid (known as a ‘goitre’).
I remember learning in medical school that goitres were common in places far from the sea where little iodine-rich foodstuffs (such as fish and seafood) are consumed in general terms. This concept came flooding back to me some years ago when I was lecturing in the US and was staying in a hotel which was also inhabited by teenage girls from a (I think) girl guide like organisation based somewhere in the mid-west in the US. I remember remarking to a colleague that every single one of these girls appeared to have a goitre.
If iodine deficiency is so common, could it be contributing to the ‘obesity epidemic’? We may not know the answer to that question for sure, but I think it’s fair to say iodine deficiency will not be helping. And anything that impacts of thyroid function won’t just impact on weight, either, remember. The BBC report makes the point that iodine deficiency can impair brain development in the foetus too.
Ensuring adequate iodine intake does appear to be a matter of considerable importance, particularly for women of child-bearing age. I found what looks like a useful resource on-line for more information about this in the form of the International Council for the Control of Iodine Deficiency Disorders. This website has a useful ‘frequently asked questions’ section which gives advice on several relevant issues including recommended daily intakes and potential iodine sources. It should perhaps be borne in mind that vegetarians and vegans are at a significantly increased risk of eating a diet deficient in iodine [2,3].
References:
1. Vanderpump M, et al. Assessment of the UK iodine status: a National Survey. Endocrine Abstracts 2011;25 OC3.8
2. Remer T, et al. Increased risk of iodine deficiency with vegetarian nutrition. Br J Nutr. 1999;81(1):45-9.
3. Krajcovicová-Kudlácková M, et al. Iodine deficiency in vegetarians and vegans. Ann Nutr Metab. 2003;47(5):183-5.
