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Changes in the prevalence of hypothyroidism: the HUNT Study in Norway

Bjørn Olav Åsvold, Lars J Vatten, and Trine Bjøro

Objective

Untreated hypothyroidism is common in iodine-replete areas. Frequent thyroid function testing and use of levothyroxine treatment for subclinical hypothyroidism suggest that the prevalence may have decreased. Therefore, in this study, we examined changes in the prevalence of hypothyroidism in a Norwegian county from 1995–1997 to 2006–2008.

Design

Population surveys of 33 917 individuals in 1995–1997 and 49 180 individuals in 2006–2008 were carried out.

Methods

We compared the prevalence of untreated overt, untreated subclinical, and treated hypothyroidism between 1995–1997 and 2006–2008.

Results

The prevalence of untreated overt hypothyroidism among women decreased by 84% from 1995–1997 (0.75%) to 2006–2008 (0.12%) (prevalence ratio (PR) 0.16; 95% CI 0.10–0.26). The corresponding decrease among men was 43% from 0.21 to 0.12% (PR 0.57; 95% CI 0.28–1.16). The prevalence of untreated subclinical hypothyroidism decreased by 64% from 3.0 to 1.1% in women (PR 0.36; 95% CI 0.31–0.42) and decreased by 54% from 2.1 to 1.0% in men (PR 0.46; 95% CI 0.38–0.56). Conversely, the prevalence of treated hypothyroidism among women increased by 60% from 5.0 to 8.0% (PR 1.60, 95% CI 1.50–1.71), and the corresponding prevalence in men doubled from 1.0 to 2.0% (PR 1.96; 95% CI 1.59–2.41). The prevalence of any form of hypothyroidism remained essentially similar at 9% in women and 3% in men.

Conclusions

The prevalence of untreated hypothyroidism in this Norwegian county decreased strongly from 1995–1997 to 2006–2008. The findings suggest that the prevalence of untreated hypothyroidism in populations with easy access to thyroid function testing and levothyroxine treatment may now be low.

Free access

Associations of TSH levels within the reference range with future blood pressure and lipid concentrations: 11-year follow-up of the HUNT study

Bjørn Olav Åsvold, Trine Bjøro, and Lars J Vatten

Objective

In cross-sectional studies, TSH levels within the reference range have been positively associated with blood pressure and adverse serum lipid levels. In a prospective study, we aimed to determine whether differences in TSH levels within the reference range are associated with future levels of blood pressure and lipids.

Design

We conducted a prospective population-based study.

Methods

In 9709 women and 4644 men without previous thyroid disease who had a baseline TSH level of 0.45–4.5 mU/l, we studied the associations of baseline TSH levels with blood pressure and lipid levels at follow-up 11 years later.

Results

Higher TSH levels at baseline were associated with higher systolic (P=0.002 in women) and diastolic (P=0.03 in women) blood pressure, non-HDL cholesterol (P=0.01 in men) and triglyceride (P=0.008 in men) levels and lower HDL cholesterol levels (P<0.001 in women and men) at follow-up, but the associations were very modest and not consistent between the sexes. Among people who remained free of thyroid disease, changes in TSH levels during follow-up were associated with concomitant changes in systolic and diastolic blood pressure, non-HDL cholesterol and triglyceride levels (all P<0.001), with similar results being observed for women and men. Thus, blood pressure and lipid levels increased among people with an increase in TSH levels and decreased among people with a decrease in TSH levels compared with people with no change in TSH levels.

Conclusions

High TSH levels within the reference range may be associated with modestly higher future levels of blood pressure and adverse serum lipids. TSH levels may co-vary with blood pressure and lipid levels among people with apparently normal thyroid function.

Free access

Association of thyroid function with estimated glomerular filtration rate in a population-based study: the HUNT study

Bjørn Olav Åsvold, Trine Bjøro, and Lars J Vatten

Objective

Low thyroid function may be associated with reduced glomerular filtration rate (GFR). We therefore studied the association of thyroid function with estimated GFR (eGFR) in a population-based study.

Design

A cross-sectional, population-based study of 29 480 individuals above 40 years of age, without previously known thyroid disease.

Methods

We calculated geometric mean eGFR and odds ratio (OR) of chronic kidney disease (CKD; eGFR <60 ml/min per 1.73 m2) according to categories of thyroid function, using people with TSH in the lower third of the reference range (0.50–1.4 mU/l) as the comparison group.

Results

TSH within the reference range (0.50–3.5 mU/l) was negatively associated with eGFR (P for trend <0.001). Compared with people with TSH in the lower third of the reference range (83.0 ml/min per 1.73 m2), eGFR was lower in people with TSH in the middle (81.6 ml/min per 1.73 m2) and highest third (80.3 ml/min per 1.73 m2) of the reference range, and in people with subclinical (79.3 ml/min per 1.73 m2, P<0.001) or overt hypothyroidism (76.5 ml/min per 1.73 m2, P<0.001). The prevalence of CKD was higher in people with TSH in the middle (OR 1.20, 95% confidence interval (CI) 1.07–1.35) or highest third (OR 1.31, 95% CI 1.13–1.52) of the reference range, compared with people in the reference group. Also, CKD was more common in people with subclinical (OR 1.63, 95% CI 1.38–1.93) or overt (OR 1.98, 95% CI 1.22–3.20) hypothyroidism.

Conclusions

These findings suggest that low thyroid function, also within the clinically normal range, is associated with reduced GFR.

Free access

Association of thyroid function with estimated glomerular filtration rate in a population-based study: the HUNT study

Bjørn Olav Åsvold, Trine Bjøro, and Lars J Vatten

The journal and the authors apologise for an error in this article published in the European Journal of Endocrinology (2011) 164 101–105. The caption to on page 104 was wrongly printed and the correct caption and table is printed in full below.

Table 4

Geometric mean eGFR (ml/min per 1.73 m2) by categories of thyroid function and age, adjusted for sex, age and smoking.
Age <70 years (n=22 071) Age ≥70 years (n=7409)
eGFR 95% CI eGFR 95% CI
Hyperthyroidism
Overt 120.5 113.5 128.0 87.0 78.9 96.0
Subclinical 91.7 89.9 93.4 76.4 73.4 79.5
TSH (mU/l)
0.50–1.4 89.9 89.6 90.3 75.3 74.4 76.2
1.5–2.4 88.5 88.1 88.9 73.5 72.6 74.4
2.5–3.5 87.0 86.3 87.7 72.6 71.4 73.8
Hypothyroidism
Subclinical 86.5 85.5 87.4 70.7 69.3 72.2
Overt 83.3 80.5 86.4 68.3 63.3 73.6

Free access

Does thyroid function influence fracture risk? Prospective data from the HUNT2 study, Norway

Anders Svare, Tom Ivar Lund Nilsen, Bjørn Olav Åsvold, Siri Forsmo, Berit Schei, Trine Bjøro, and Arnulf Langhammer

Objective

To prospectively study the relation between TSH and risk of hip and forearm fractures.

Design

A population-based cohort study.

Methods

In a substudy of the second survey of the Nord Trøndelag Health Study, Norway (HUNT2, 1995–97), linked with a hospital-based fracture registry, we investigated the relation between baseline TSH and risk of hip and/or forearm fractures.

Population

A total of 16 610 women and 8595 men aged 40 years or more, without previous self-reported thyroid disease and hip or forearm fractures.

Results

During 12.5 years follow-up, a total of 1870 women and 342 men experienced hip or forearm fractures. Overall, there was no relation between baseline TSH and fracture risk. However, there was weak evidence that women with TSH <0.5 and >3.5 mU/l had a slightly increased risk of hip fractures (hazard ratio (HR) 1.30, 95% CI 0.97–1.94 and HR 1.19, 95% CI 0.93–1.52) compared with the reference group with TSH of 1.5–2.4 mU/l. Supplementary analyses showed higher hip fracture risk in women with TSH >4.0 mU/l and negative thyroid peroxidase antibodies (TPOAb) compared with the reference group (HR 1.75, 95% CI 1.24–2.46).

Conclusion

We found no statistically significant relation between baseline TSH and subsequent fracture risk, but the data suggest a weak positive association with hip fracture risk among women with both low and high TSH. The latter association was confined to women with negative TPOAb status.