Response to Birth Weight and Retinal Vascular Changes
We thank Lim and Cheung1 for their interest in our article.2 They hypothesize that the risk of incident hypertension is greater in persons with both low birth weight and retinal arteriolar narrowing. We tested this interesting hypothesis in the Atherosclerosis Risk in Communities Study cohort, where we re-examined participants free from hypertension at the time of retinal photography and incidence of hypertension 3 years later. Details of the study population and ascertainment of incident hypertension are described elsewhere.3
Of 122 participants with low birth weight ≤2.5 kg, 19.7% (24 of 122) developed incident hypertension compared with 16.7% of participants with normal or higher birth weight (379 of 2276). There was a statistically significant interaction between birth weight and retinal arteriolar caliber on risk of hypertension (P=0.03). Among persons of low birth weight, narrower arterioles was not associated with incident hypertension (odds ratio: 1.2, 95% CI: 0.6 to 2.2; P=0.59, per SD decrease in arteriolar caliber, adjusting for age, gender, ethnicity, study center, body mass index, and smoking). Among persons of normal or higher birth weight, narrower arterioles were associated with an increased risk of incident hypertension (odds ratio: 1.5; 95% CI: 1.3 to 1.7; P<0.0001). In addition, wider venular caliber was also associated with incident hypertension, but again only in persons of normal or higher birth weight (odds ratio: 1.2; 95% CI: 1.0 to 1.3; P=0.049). We did not adjust for blood pressure, because this may constitute an overadjustment.4
Thus, we cannot confirm the hypothesis of Lim and Cheung1 that the risk of incident hypertension is greater in persons with both low birth weight and retinal arteriolar narrowing. However, our results should be interpreted with caution because of the small number of participants with low birth weight, many of whom already developed hypertension by the time of the study. In this adult population, the increased susceptibility of low birth weight and arteriolar narrowing on hypertension risk may have been fully realized. It should also be noted that other mechanisms (eg, reduced nephron numbers) may also contribute to the low birth weight and hypertension association.4
Lim and Cheung1 further highlighted the association of low birth weight with wider retinal venules in young Asian children free from confounding factors and suggest that the association of birth weight and retinal vessel caliber may vary by ethnicity. This is an interesting suggestion, but there is little evidence that the association of birth weight, or retinal vessel calibers, with future hypertension varies by ethnicity. We found the same association of lower birth weight with narrower retinal arterioles in both white and black subjects in the Atherosclerosis Risk in Communities Study. We did observe an association of wider venules with incident hypertension, although venular caliber was not related to birth weight in the Atherosclerosis Risk in Communities Study population. More work is certainly needed to examine the effects of birth weight on novel retinal measures of microvascular architecture and how this relates to hypertension and cardiovascular disease pathogenesis and risk.
Sources of Funding
This study is supported by National Heart, Lung, and Blood Institute contracts N01-HC-55015, N01-HC-55016, N01-HC-55018, N01-HC-55019, N01-HC-55020, N01-HC-55021, N01-HC-55022. Additional support was provided by NHLBI grant R21-HL077166.