Introduction

negative correlation for FEV1 while the others showed a positive correlation. This implies that the greater the urinary Cd the lower the FEV1 among smokers.

A graph (figure 3) in which the log of the Cadmium creatinine ratio was categorized and the mean FEV1 and FVC in these categories was plotted. This revealed a decline in both parameters (FEV1 and FVC) as the log Cd/Cr ratio was increasing.

Table7.

Linear Regression of Urinary Cadmium and FEV1, FVC and FEV1/FVC among smokers

Parameter Coefficients p 95.0% CI

Constant 12.75 0.987 -1545.13 1570.63

FEV1(L) -159.72 0.509 -636.25 317.80

FVC(L) 65.28 0.753 -343.54 474.12

FEV1/FVC (%) 4.27 0.636 -13.49 22.03

Dependent variable: Urinary Cd ug/L

P < 0.05 is considered statistically significant

Figure3.

C h a pt er

Fi ve

5.0 Dis cus sio n, conclusions and recommendations.

5.1 Discussion

The relationship between the FEV1, FVC and the log of the ratio of Cadmium to creatinine among smokers.

This cross-sectional study looked at the ventilatory function among smokers and non-smokers.

Their urinary cadmium levels were determined and a relationship was found to exist between the ventilatory function and the total body cadmium using urinary cadmium as a surrogate, it revealed that increased urinary cadmium was associated with a reduction in ventilatory function parameters.

5.1.1 Ventilatory function

The FEV1, FVC and Ratio of FEV1 to FVC showed a decrease among the subjects (smokers) when compared to the controls (non-smokers). There was a significant decline in the FEV1 which was similar with studies done by Litonjuo etal²⁷, Mannino et al²⁸ and Lampe²⁹ et al. The ratio of FEV1 to FVC did not show a significant difference between the controls and the subjects, this may be because the average pack years in this study fell within the level for moderate smokers and could account for the lack of significant difference between the groups as the other studies mentioned showed a much higher number of pack years. The study by Lampe et al²⁹used 30 pack years as the cutoff between heavy smokers and light smokers. Lin etal⁸¹only assessed smokers with 20 pack years and above as being heavy smokers. In the study by Mannino et al²⁸ smokers with a 40-50 pack year history had a mean decline of 3.2% between those in the 90^th percentile and those in the 10^th percentile. It is known that lung function declines with age and cigarette smoking accelerates this decline. The prevalence of an obstructive pattern was twice as much in subjects aged 55years and above than in those aged 40-54.The mean age in the study by Litonjuo et al²⁷ was 67.5 (6.4) year while this study had a younger mean age. This could also account for the higher prevalence of an obstructive pattern in their studies.

There was a significant difference in the PEF between the subjects and controls. Smokers were found to have a mean PEF of 408.29 (113.68) and 468.76 (121.35) p=0.00, this seems to correlate with the FEV1 findings. Similar studies done by other researchers^27-29,84 in more developed countries did not measure the PEF. Some researchers in Nigeria like Ukoli and colleagues⁷² compared PEF among smokers and

non-smokers (both male and female) and got a mean PEF of 225 (62.79) p<0.05 among non-smokers which was significantly lower than that among smokers. Obaseki et al⁷⁰ also tried to correlate peakflow and spirometric findings among a cohort of patients with COPD to monitor their health related quality of life and found peak flow a useful tool especially in resource poor countries like Nigeria.

5.1.2 Urinary Cadmium

The urinary cadmium showed a dose related relationship with the number of cigarettes smoked calculated as pack years. The log of the Cd creatinine ratio showed a significant difference between the subjects and the controls. This compared with studies done by Mannino etal²⁸ which showed that current smokers had higher mean urinary cadmium/creatinine levels (0.46 micro g/g) than former (0.32 micro g/g) or never smokers (0.23 micro g/g), another study by Lin etal⁸⁴showedgeometric means for urinary Cd were 0.87, 0.53, and 0.36 μg/g creatinine in active smokers, former smokers, and never-smokers, respectively. In this study a dietary history was not taken as it is known that some foods e.g.

dairy products, high fiber diets can increase the body burden of cadmium¹⁵. The study done by Mannino et al²⁸ looked into the dietary history of their patients but did not report any significant difference among the subjects. Moreover some studies put absorption of inhaled cadmium at 30 to 60%^19,20 , others like that by Yu⁸⁵ shows that 25 to 40% of inhaled Cd is retained while only 5 to 10% of ingested Cd is absorbed. Other conditions such as decreased iron levels can increase cadmium absorption from the gastrointestinal tract and thus increase the total body Cadmium burden⁴². Various studies have consistently shown that cigarette smoking increases significantly the total burden of Cadmium.^86-87There appears to be a dose related relationship with the number of pack years.

Smoking intensity has also been found to increase the total burden of Cadmium²⁸. The deeper the inhalation, the greater the amount of cadmium deposited in the lungs. About 10-20% of cadmium in cigarettes is inhaled⁸⁸, this may be one of the factors that may account for some of the variability

between lung function among those with similar number of pack years, age, height, etc and marked differences in lung function.

5.1.3 Lung function and Urinary Cadmium

The linear regression model showed an inverse relationship between the urinary cadmium and lung function generally (Fig 2) but in this study the significant lung function parameter was the FEV1. This correlates with the study done by Lampe et al ²⁷, which showed a stronger correlation between Urinary cadmium and FEV1 than with FVC or the ratio of FEV1 to FVC.

This is unlike the study by Mannino etal²⁸ which found a significant relationship between the urinary Cd and FEV1, FVC and theFEV1/FVC ratio. This could be due to the relatively smaller number of pack years and the younger age as has been mentioned earlier and the larger study population. The Cd content of cigarettes manufactured in Nigeria has been found to vary as different studies seem to show conflicting data. In a study by Nnorom and others⁷ the Cd concentrations were found in imported brands to be 1.52 (0.46) µg/g compared to the Nigerian brands 1.10 (0.35) µg/g. While in another study done by Uwakwe and Ibiam⁸⁸ in Abakaliki south eastern Nigeria revealed that Nigerian cigarettes had a statistically significant higher Cd content than imported cigarettes and the cadmium levels varied depending on the type of cigarette smoked, they also discovered that the there was no relationship between the amount of tobacco contained in each brand of cigarette and the cadmium content. This means that different types of tobacco leaves, the method of growth and the manufacturing process may affect the concentration of Cd. Further research would be necessary to ascertain the cadmium levels of the population at large and that of smokers in different cohorts to determine if there is a significant difference in total cadmium burden across them in relation to their exposure pattern.