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The Journal of Clinical Endocrinology & Metabolism Vol. 86, No. 4 1518-1524
Copyright © 2001 by The Endocrine Society

From the Clinical Research Centers

Effects of Growth Hormone (GH) Administration on Homocyst(e)ine Levels in Men with GH Deficiency: A Randomized Controlled Trial1

Gemma Sesmilo2, Beverly M. K. Biller, Joan Llevadot2, Douglas Hayden, Greta Hanson, Nader Rifai and Anne Klibanski

Neuroendocrine Unit and General Clinical Research Center, Massachusetts General Hospital and Harvard Medical School; Cardiovascular Division, Brigham and Women’s Hospital and Harvard Medical School (J.L.); and Departments of Laboratory Medicine and Pathology, Children’s Hospital and Harvard Medical School (G.H., N.R.), Boston, Massachusetts 02114

Address all correspondence and requests for reprints to: Anne Klibanski, M.D., Neuroendocrine Unit Massachusetts General Hospital, Fruit Street, Bulfinch 457B, Boston, Massachusetts 02114. E-mail: aklibanski{at}partners.org


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
GH deficiency is associated with increased cardiovascular mortality and early manifestations of atherosclerosis. Elevated serum homocyst(e)ine levels have been found to be associated with increased cardiovascular risk. The effect of GH replacement on homocyst(e)ine has not been investigated to date. We evaluated the effect of GH replacement on fasting homocyst(e)inemia in a group of men with adult-onset GH deficiency in a randomized, single blind, placebo-controlled trial.

Forty men with adult-onset GH deficiency were randomized to GH or placebo for 18 months, with dose adjustments made according to serum insulin-like growth factor I (IGF-I) levels. Fasting serum homocyst(e)ine, folate, vitamin B12, and total T3 levels were determined at baseline and 6 and 18 months. Anthropometry, IGF-I levels, insulin, and glucose were measured at 1, 3, 6, 12, and 18 months. Nutritional assessment, body composition, total T4, thyroid hormone binding index, and free T4 index were assessed every 6 months.

Homocyst(e)ine decreased in the GH-treated group compared with that in the placebo group (net difference, -1.2 ± 0.6 µmol/L; confidence interval, -2.4, -0.02 µmol/L; P = 0.047). Homocyst(e)ine at baseline was negatively correlated with plasma levels of folate (r = -0.41; P = 0.0087). Total T3 increased in the GH-treated group vs. that in the placebo group (net difference, 0.17 ± 0.046 ng/dL; confidence interval, 0.071, 0.26 nmol/L; P = 0.0012). Folate and vitamin B12 levels did not significantly change between groups. Changes in homocyst(e)ine were negatively correlated with changes in IGF-I. For each 1 nmol/L increase in IGF-I, homocyst(e)ine decreased by 0.04 ± 0.02 µmol/L (P = 0.029). In contrast, changes in homocyst(e)ine did not correlate with changes in folate, vitamin B12, total T3, C-reactive protein, interleukin-6, or insulin levels. This study shows that GH replacement decreases fasting homocyst(e)ine levels compared with placebo. This may be one of the mechanisms involved in the putative modulation of atherosclerosis and cardiovascular risk by GH replacement.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
GH DEFICIENCY in adults is thought to be associated with increased cardiovascular mortality and early manifestations of atherosclerosis (1, 2, 3). Endothelial dysfunction and increased number of atheromatous plaques have been found in GH-deficient patients (4, 5, 6). Recently, two prospective studies have reported that GH administration decreases intima-media thickness, an indicator of atherosclerosis (4, 7). Therefore, it has been hypothesized that GH replacement may have beneficial cardiovascular effects, but the mechanisms by which GH affects the atherosclerotic process are unclear.

GH-deficient adults have a high incidence of cardiovascular risk factors, including obesity with central fat distribution, hypercholesterolemia, and insulin resistance (8, 9, 10). GH replacement has been reported to decrease central fat (11), but its effects on lipids are controversial (12). Insulin resistance increases acutely with GH replacement, but some studies have suggested reversal of this effect with long-term therapy (13). We recently reported that GH replacement is associated with a decrease in inflammatory markers of cardiovascular risk (14), but it has not been explored to date how GH administration may affect other pathways involved in atherosclerosis and thrombosis, such as homocysteine metabolism.

In the last decade there has been a great deal of interest in the relationship between moderate increases in homocyst(e)ine and cardiovascular risk. Homocysteine is a nonprotein-forming sulfur amino acid produced during catabolism of the essential amino acid methionine (15). Homocysteine is oxidized in plasma to homocystine and cysteine-homocysteine. Serum or plasma total homocysteine, also termed homocyst(e)ine, is the sum of the three compounds (16). Human and animal studies support the concept that elevated homocyst(e)ine may be an independent risk factor for atherosclerosis and thrombosis (15). Patients with homocystinuria, who present with severe hyperhomocyst(e)inemia, experience thromboembolic events at an early age (17), and methionine-induced hyperhomocyst(e)inemia in healthy human subjects causes endothelial dysfunction (18). Although data are conflicting, a number of prospective studies have reported that plasma homocyst(e)ine levels in apparently healthy individuals predict risk of clinical cardiovascular events as well as cardiovascular mortality (19, 20, 21, 22, 23, 24, 25). Several studies have shown that folate supplements with or without vitamins B6 and B12 decrease homocyst(e)ine levels in humans (26, 27). Furthermore, the reduction in homocyst(e)ine with folate, B6, and B12 administration has been recently reported to reduce the rate of progression of carotid plaque area, suggesting a beneficial effect of a reduction in homocyst(e)ine in the atherosclerotic process (26).

Hormonal influences such as estrogen and thyroid hormone are known to affect homocyst(e)ine levels (28), but the possible effect of GH on homocyst(e)ine has not been investigated to date. Given the anabolic properties of GH and its effects on increasing protein synthesis and muscle mass, we hypothesized that GH administration may affect homocyst(e)ine levels. Therefore, we investigated the effects of GH replacement therapy on homocyst(e)ine, folate, and vitamin B12 serum levels in a group of men with adult-onset GH deficiency in whom other cardiovascular variables have been previously reported (14, 29). Correlations between homocyst(e)ine and inflammatory cardiovascular risk markers have also been explored. In addition, because GH stimulates the peripheral conversion of T4 to T3, and thyroid hormone is known to affect homocyst(e)ine, we also investigated thyroid hormone levels and their relationship to homocyst(e)ine during the study.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Details of the complete protocol and other results from this study have been previously published (14, 29, 30).

Study subjects

Forty men, 24–64 yr old (mean, 49 yr), with a history of adult-onset pituitary disease were recruited. All patients met the following criteria: 1) normal growth and development; 2) benign sellar neoplasm, pituitary apoplexy, or idiopathic hypopituitarism diagnosed after age 18 yr; and 3) peak GH less than 5 µg/L after two pharmacological stimuli on different days (including insulin tolerance test and arginine when insulin tolerance test contraindicated). Patients were excluded if a history of malignancy, acromegaly, or diabetes was present, or if they had not been stable and receiving appropriate replacement for other hormonal deficiencies for at least 6 months. All of the patients who met the criteria and were willing to participate entered the study.

Study design

The study was an investigator-initiated, single center, randomized, single blind, placebo-controlled trial. It was approved by the subcommittee on human studies of the Massachusetts General Hospital, and patients gave written informed consent. After baseline evaluation, patients were randomly assigned to GH or placebo for 18 months. Follow-up visits were at 1 week and 1, 3, 6, 12 and 18 months of treatment. Anthropometry and insulin-like growth factor I (IGF-I) levels were determined at 1, 3, 6, 12, and 18 months. Nutritional intake, body composition, creatinine, total T4, and thyroid hormone binding index (THBI) were assessed every 6 months. Homocyst(e)ine, folate, vitamin B12, and total T3 were measured at baseline and 6 and 18 months. C-Reactive protein, interleukin-6, glucose, and insulin were also measured as previously reported (14) and were used in the correlation analysis of the main outcome variable. All patients came for every visit to the General Clinical Research Center of Massachusetts General Hospital, where fasting samples were collected and processed uniformly pre- and posttreatment according to written physician’s orders. Blood samples were obtained from a forearm vein in red-topped tubes. Samples were allowed 30 min to clot and were centrifuged at 4 C, and serum was frozen until assayed. Although homocyst(e)ine in whole blood may increase due to red cell production, the increase is minimal if the sample is processed within 1 h (31). Homocyst(e)ine, folate, vitamin B12, C-reactive protein, and interleukin-6 were measured from frozen serum aliquots that had been stored for 3–6 yr at -20 C without prior thawing.

Participants were assigned by a computer-generated randomization schedule to self-administer either daily sc recombinant human GH injections (Nutropin, Genentech, Inc., South San Francisco, CA) or placebo (identically presented and composed of the same vehicle used for GH) at bedtime for 18 months. The computerized randomization, performed by Genentech, Inc. (San Francisco, CA), stratified patients with respect to age. The randomization code was revealed only to the study physician and was kept in a separate file. Patients and all other personnel involved in the study were unaware of the treatment assignment. The starting dose of GH was 10 µg/kg·day, and the dose was subsequently adjusted to maintain IGF-I levels in the age-gender normal range for each patient. Placebo patients were also asked to make dose adjustments to maintain blinding.

Measurements

Nutritional intake was evaluated at baseline with 7-day food records. Nutrient calculations were performed using the Nutrition Data System software, developed by the Nutrition Coordinating Center, University of Minnesota (Minneapolis, MN). Body composition (lean body mass and percentage of body fat) was determined by dual energy x-ray absorptiometry (QDR-2000, Hologic, Inc., Waltham, MA) and has been previously reported (29). Serum IGF-I levels were measured by RIA after acid-alcohol extraction (Nichols Institute Diagnostics, San Juan Capistrano, CA). Glucose, insulin, serum total T3, total T4, THBI, and creatinine measurements were performed at Massachusetts General Hospital as described previously (32). The free T4 index was calculated as the product of total T4 and THBI. Homocyst(e)ine was measured by high performance liquid chromatography with fluorometric detection (33). The interassay coefficient of variation at concentrations of 7 and 12 µmol/L were 3.3% and 2.9%, respectively. Folate and B12 levels were measured by a competitive magnetic separation assay on the Immuno-1 analyzer (Bayer Corp., Tarrytown, NY). The interassay coefficients of variation over a wide range of concentrations for folate and B12 were 7% and 4%, respectively. C-Reactive protein was measured using the Behring BNII analyzer (Dade Behring, Newark, DE) by an ultrasensitive and latex-enhanced immunotechnique. The interassay coefficient of variation was 5.6% over a wide range of concentrations. Interleukin-6 was measured by an ultrasensitive ELISA assay from R&D Systems (Minneapolis, MN) with an interassay coefficient of variation of 5.8%.

Statistical analysis

The outcome of interest was change from baseline. A primary analysis using repeated measures analysis of covariance (SAS PROC MIXED) was performed, controlling for baseline value and month to estimate the mean change in outcome variables from baseline within and between groups. Unless otherwise noted, results from the primary analysis are reported as the difference in the mean change from baseline at months 6 and 18 ± SE between the two treatment groups with 95% confidence intervals. P values for comparison between groups are also reported. In a secondary analysis, repeated measures analysis of covariance controlling for baseline was used to test for a time by treatment interaction over months 6 and 18. Repeated measures analysis of covariance was used to test for correlation between changes in variables. We used Student’s two-tailed t test to compare baseline values. Correlation between baseline variables was estimated using Pearson product-moment correlation coefficients. The analysis was performed following the intention to treat principle, and all data available were considered. Two-sided P < 0.05 was considered significant. SAS 8 and JMP 3.2.2 (SAS Institute, Inc., Cary, NC) were used for all data analysis.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Clinical and biochemical characteristics at baseline are shown in Table 1Go. The majority of patients had GH deficiency resulting from pituitary adenoma. There were no differences between groups in blood pressure, smoking history, dyslipidemia history, or serum levels of any of the parameters assessed at baseline. One patient in the GH-treated group had a history of coronary artery disease. No subject was taking niacin, theophyline, phenytoin, or carbamazepine. Seven patients, four in the GH and three in the placebo groups, respectively, dropped out of the study. Four (two in each group) dropped out before month 6, and their results are not included in the follow-up analysis.


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  		Table 1. Clinical and biochemical characteristics at baseline

 
The initial GH dose of 10 µg/kg·day was reduced in all patients based on elevated serum IGF-I levels. The mean dose at 18 months was 4 ± 2 µg/kg·day. The mean IGF-I level at 18 months was 42.2 nmol/L (range, 29.7–61.3; normal, 11.8–47.2).

Nutritional assessment

Dietary intake of proteins, folate, vitamin B6, and vitamin B12 did not differ at baseline between groups (Table 1Go). Mean folate intake at baseline was 343 ± 162 (±SD) µg/day (median, 323 µg/day) for all patients. Only 33% of subjects had folate intakes above the 400 µg current recommended daily allowance (RDA) (34), whereas 80% had intakes above the prior RDA of 200 µg/day. Ninety-four percent of patients had B12 intakes above the 2.4 µg/day RDA, and 76% of patients had B6 intake above the 1.3 mg/day RDA. Two patients (one in each treatment group) were taking vitamin B12 at baseline, and this was maintained during the 18 months of the study. One other patient (in the placebo group) took a multivitamin only at baseline, and two other patients (one in each group) took vitamin B12 from months 6–18 and 12–18, respectively. The two groups were balanced regarding supplemental vitamin intake. Changes in folate, B12, and B6 intake estimated with the 7-day food diary were not different between the two groups (Table 2Go).


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  		Table 2. Changes from baseline within and between groups

 
Homocyst(e)ine, folate, and B12 levels

The mean homocyst(e)ine at baseline in the entire patient group was 11.6 ± 3.1 (±SD) µmol/L (median, 12.3 µmol/L; range, 3.7–19.4). Homocyst(e)ine levels have been reported in a large cross-sectional study of U.S. adults in the Third National Health and Nutrition Examination Survey (NHANES III) (35), which used the same methodology as in the current study. The median homocyst(e)ine level in the GH-deficient patients in the present study is almost identical to the reported 90th percentile of a comparable subset from NHANES III (male, 40–59 yr old, vitamin replete). Both the present study and NHANES III were completed before 1997, before fortification of grain products with folic acid. The median folate level at baseline was 12.3 nmol/L (range, 4.1–61.2).

Homocyst(e)ine at baseline was negatively correlated with plasma levels of folate (r = -0.41; P = 0.0087). There was no baseline correlation between homocyst(e)ine and folate intake, serum B12 levels, B12 intake, B6 intake, serum creatinine, dietary protein intake, lean body mass, IGF-I, total T3, or free T4 index levels. All patients had creatinine values in the normal range throughout the study. No correlation was noted between homocysteine and C-reactive protein or interleukin-6.

Homocyst(e)ine decreased in GH-treated patients vs. placebo [net difference, -1.2 ± 0.6 µmol/L; confidence interval (CI), -2.4, -0.02; P = 0.047; Fig. 1Go and Table 2Go], whereas the changes in serum vitamin B12 levels did not differ between groups (3.1 ± 18.4 pmol/L; CI, -34.4, -40.5; P = 0.87; Table 2Go). Serum folate increased within the GH-treated group (4.8 ± 1.4 nmol/L; CI, 1.9, 7.7; P = 0.002; Fig. 2Go). The difference between the GH and placebo groups (3.7 ± 2.0 nmol/L; CI, -0.4, 7.7; P = 0.073) showed a trend but did not reach statistical significance (Table 2Go). Changes in serum folate were not correlated with changes in folate intake, IGF-I, total T3, or free T4 index.



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  		Figure 1. Changes in homocyst(e)ine levels in the two treatment groups. •, GH-treated patients; {circ}, placebo-treated. The P value for comparison between groups is 0.0473. Error bars represent the SEM.

 


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  		Figure 2. Changes in serum folate in the two treatment groups. •, GH-treated patients; {circ}, placebo-treated patients. The P value for comparison between groups is 0.0731. Error bars represent the SEM.

 
Total T3, total T, free T4 index, and THBI

Total T3 levels increased in the GH-treated group vs. placebo (net difference, 0.17 ± 0.05 nmol/L; CI, 0.07, 0.26; P = 0.0012; Fig. 3Go and Table 2Go), although none of the patients had total T3 values above the normal range at months 6 and 18. There were no differences between groups in the changes in total T4 and free T4 index (Table 2Go). GH-treated patients had a significant decrease in free T4 index (-8.06 ± 3.05; CI, -14.3, -1.8; P = 0.013) in the analysis within group. Three patients had free T4 index below the normal range at month 6, but none at month 18.



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  		Figure 3. Changes in total T3 levels (A) and FT4I (B) in the two treatment groups. •, GH-treated patients; {circ}, placebo-treated patients. the P value for comparison between groups is 0.0012 for total T3 and 0.14 for FT4I. Error bars represent the SEM.

 
Correlation between changes in homocyst(e)ine and changes in covariates

Changes in homocyst(e)ine did not correlate with changes in total T3, free T4 index, lean body mass, creatinine, insulin, glucose, or the insulin to glucose ratio. Similarly, no correlation between changes in homocysteine and changes in the inflammatory markers C-reactive protein or interleukin-6 was noted. There was no correlation between changes in homocysteine and changes in plasma folate or vitamin B12 levels. In contrast, changes in homocysteine were negatively correlated with changes in IGF-I; for each 1 nmol/L increase in IGF-I, homocysteine decreased by 0.04 ± 0.02 µmol/L (P = 0.029).

Time by treatment interaction

Total T3 showed a significant time by treatment interaction between months 6 and 18, consistent with a greater difference between the two groups at month 6 than at month 18. There was no significant time by treatment interaction in any of the other outcome variables studied including homocyst(e)ine, consistent with no change over time in the effect of GH on those variables.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
We have studied the effect of chronic GH replacement on serum levels of homocyst(e)ine in men with adult-onset GH deficiency. These results show for the first time that GH replacement is associated with a decrease in serum homocyst(e)ine. This may be a factor involved in the putative GH modulation of atherosclerosis.

Atherosclerosis is a multifactorial disease. Moderate elevations in homocyst(e)ine plasma levels are thought to play an independent role in the risk of cardiovascular events (15). Although there are contradictory conclusions from prospective epidemiological studies regarding the association of moderately elevated plasma levels of homocyst(e)ine with the incidence of cardiovascular events (36), there are human and animal data supporting a pathogenetic role of homocyst(e)ine in vascular disease. Homocystinuric patients who have severe hyperhomocyst(e)inemia present with thromboembolic episodes at early ages (17). Experiments in healthy subjects have demonstrated that acute hyperhomocyst(e)inemia, produced by an oral methionine load, causes endothelial dysfunction (18, 37, 38) even when small physiological increments in plasma homocyst(e)ine are induced (39). Randomized studies in animals have shown that hyperhomocyst(e)inemia causes abnormal vascular reactivity in nonhuman primates (40) and frank atherothrombosis in minipigs (41). Moreover, the reduction of homocysteine with vitamin therapy in human subjects has recently been reported to decrease progression of carotid plaque area (26).

The median homocyst(e)ine level at baseline in the GH-deficient patients in the present study was in the 90th percentile of the distribution of a similar population reported in NHANES III (35). Although study comparisons have limitations, the sample collection method and the assay described for homocyst(e)ine in NHANES III are the same as those used in the present study. This indicates that the levels of homocyst(e)ine in our patients were high at baseline, in a range associated with high cardiovascular risk (19, 20, 21, 23, 24, 25). With GH treatment, homocyst(e)ine levels decreased by nearly 8%. The clinical significance of the magnitude of this decrement is not yet certain. Interestingly, these results are similar to those recently reported for hormone replacement therapy with estrogen and raloxifene when administered to healthy postmenopausal women (42).

There are several hypotheses to explain the GH effect on homocyst(e)ine levels. Homocysteine is formed during the catabolism of the essential amino acid methionine. Its metabolism occurs by two main pathways: transulfuration to cysteine and remethylation to methionine. The first process uses pyridoxal phosphate, the active form of vitamin B6, as a cofactor. Alternatively, in cases of negative methionine balance, the remethylation pathway is activated, resulting in the synthesis of methionine, a process that requires vitamin B12 and folate as cofactors (43). GH is an anabolic hormone that stimulates protein synthesis (44). In accordance with other studies, we have previously reported in this group of patients that 18 months of GH replacement increased lean body mass and bone mineral density at different sites (29, 45). Both processes implicate an increase in protein synthesis. It is interesting to speculate that the stimulation of protein synthesis may be associated with an increased requirement for methionine and cysteine, which may cause an acceleration of homocysteine metabolism and consequently a reduction in plasma levels of homocyst(e)ine.

Another consideration when evaluating GH effects on homocyst(e)ine in hypopituitary patients would be the action of GH on the bioavailability of other hormones such as T4. GH administration in adults receiving thyroid replacement therapy is known to accelerate the metabolism of T4 to T3 (46). This may cause a transient decrease in total and free T4 and an increase in T3 levels. Hypothyroidism is associated with elevated homocyst(e)ine levels (47), and normalization of thyroid status with T4 has been reported to decrease homocyst(e)ine in a recent open label study (48). We evaluated the effect of GH treatment on thyroid hormone levels. GH therapy increased total T3 levels compared with placebo, although T3 levels at the 6 and 18 month visits were within the normal range for all patients. Moreover, we found a positive time by treatment interaction for total T3, but not for homocyst(e)ine, consistent with a sustained effect of GH on homocyst(e)ine, but not on total T3. It is not known whether changes in thyroid status within the normal range have any effect on homocyst(e)ine levels. In addition, changes in homocyst(e)ine were not correlated with changes in T3, whereas they were negatively correlated with IGF-I. Despite this, it remains possible that the observed changes in thyroid status may be related to the GH effect on homocyst(e)ine.

It is known that folate intake is inversely correlated with fasting homocyst(e)ine, and folate supplements have been reported to reduce homocyst(e)ine levels (27). We did not find a correlation between folate intake and homocyst(e)ine levels at baseline, perhaps due to small sample number and possible inaccuracies in folate intake estimated by the 7-day food record. Importantly, no differences in folate intake were detected between the two groups.

Serum folate levels increased within the GH-treated group. Differences in folate levels between groups showed a trend, but did not reach statistical significance. It is not known whether GH has a direct effect on folate metabolism, but no correlation was found between changes in folate and changes in IGF-I. It has been reported that thyroid hormones increase folate levels (49). In the current study T3 increased in the GH group. However, we did not find a significant correlation between changes in folate and changes in either T3 or free T4 index. Another potential explanation for the folate increase would be a difference in folate intake between the two groups. However, the randomized study design theoretically provides balance between the two groups in terms of intake. Despite this optimal study design, it is impossible to rule out completely that the increase in serum folate in the GH-treated group could be due to an increase in folate intake. Even though serum folate increased in the GH-treated group, these changes were not correlated with changes in homocysteine. In contrast, changes in homocyst(e)ine were negatively correlated with changes in IGF-I.

GH is also known to have effects on insulin resistance. We previously reported in this group of patients that GH significantly increased glucose levels throughout the 18 months of the study and increased insulin levels during the first 3 months of therapy but not during months 6–18 (14). The relationship between insulin and homocyst(e)ine is still controversial. In rats, hyperinsulinemia induced by a high fat and sucrose diet resulted in hyperhomocystein(e)mia (50), whereas in humans an inverse relationship between plasma homocyst(e)ine levels and insulin has been described only in nondiabetic individuals (51, 52, 53). Other studies have not found any relationship between homocyst(e)ine and insulin resistance (54, 55). In this study no correlation between changes in insulin, glucose, or the insulin to glucose ratio and homocyst(e)ine were observed.

Finally, we explored the correlation between the changes in homocyst(e)ine and the changes in C-reactive protein and interleukin-6, two inflammatory markers that decreased with GH treatment in this population of patients, as recently reported (14). There was no significant correlation between homocyst(e)ine and inflammatory markers, suggesting that the changes in homocyst(e)ine are probably not a reflection of changes in nonspecific inflammation.

Limitations to this study have to be considered. First, the study was based on 40 patients; studies with a larger patient population are needed to confirm our findings. Second, although the study was designed to provide physiological GH replacement, some patients had supranormal IGF-I levels, especially at the beginning of the study. We cannot rule out an effect of initially high levels on final outcome. Further studies with consistently physiological replacement are needed. Third, folate in frozen samples has been reported to be unstable. Fourth, although the randomization should have balanced the two groups in terms of folate and vitamin intake, it is not possible to rule out differences in intake between the two treatment groups that could be related to our findings. Finally, the study was limited to men, and further studies should include women.

In conclusion, we have shown that GH replacement in men with GH deficiency lowers peripheral levels of homocyst(e)ine compared with placebo. This may be one of the mechanisms by which GH affects the process of atherosclerosis with potential beneficial consequences. Given the relatively small number of patients and the single gender population, further studies are needed to confirm this association, to explore cardiovascular aspects of GH replacement in women, and to determine the long-term benefits of GH replacement on cardiovascular clinical events.


   Acknowledgments
 
We thank Howard Baum, M.D., and the General Clinical Research Center staff for patient recruitment and care, and David Schoenfeld, Ph.D., for statistical advice.


   Footnotes
 
1 This work was supported in part by NIH Grants RR-1066 and DK-08783. Back

2 Supported by Fundacio la Caixa, Barcelona, Spain. Back

Received August 10, 2000.

Revised December 18, 2000.

Accepted December 20, 2000.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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