Folic acid is a vitamin needed by a number of enzymes essential for DNA synthesis and amino acid metabolism [1]. This nutrient is an important co-factor in the methionine pathway, the most important source of methyl groups in the human organism [2]. Low folic acid intake is known to contribute to increased levels of homocysteine (Hcy) as a result of its interrelation with methionine metabolism [2–6]. Inadequate intake of folic acid has been described in athletes who practice different sports [1], and athletes are often deficient in their intake of total calories, carbohydrate, protein, and micronutrients [7]. Some authors consider supplementation with folic acid as an efficient way to reduce elevated Hcy levels [8, 9], and it has been suggested that in certain cases, folic acid supplementation should be used for preventive purposes [10]. Earlier findings have suggested that doses of 0.2 to 0.4 mg/d can achieve maximal reductions in Hcy in healthy young populations, whereas doses up to 0.8 mg/d are needed to reduce Hcy in individuals with coronary heart disease [11].

Regular physical activity (PA) can alter the requirements for some micronutrients [1]. This makes it important to choose foods carefully, taking into account the quality and quantity of macronutrient intakes, since requirements can vary depending on the type of exercise performed [12].

Elevated plasma levels of Hcy are considered a risk factor for cardiovascular disease (CVD) [13]. Regular physical activity is now well established as a key component in the maintenance of good health and disease prevention, and has been specifically recognized to reduce the risk of appearance of CVD by reducing chronic inflammation, which plays a key role in the atherogenic process, blood pressure, body composition, insulin sensitivity and psychological behavior [14, 15].

In contrast, acute intense exercise has been shown to increase plasma Hcy concentrations [14]. Several factors have been reported to be associated with increases in Hcy, such as endothelial cell injury, which stimulates vascular smooth muscle cell growth, increases platelet adhesiveness, enhances LDL cholesterol oxidation and deposition in the arterial wall, and directly activates the coagulation cascade [16]. Some research has concluded that Hcy levels may be influenced by the duration, intensity and type of exercise [6, 14, 17, 18], whereas other studies have identified lifestyle factors such as smoking, eating habits and alcohol consumption [6, 19, 20], as well as age, elevated blood pressure, renal failure [17, 21] and genetic factors [22], as factors that contribute to increased plasma concentrations of Hcy. In addition, nutritional factors such as reduced folic acid intake have been implicated [3, 13].

Several authors [4, 13, 22, 23] have established a direct relationship between regular physical exercise (PA) and a reduction in CVD risk, although the data regarding the effect of PA on plasma Hcy concentrations remain controversial because of methodological differences among different studies. Murakami et al. [13] noted that these discrepancies may reflect differences in the methods used to evaluate PA, the lack quantitative information on training intensity or training time, and in some cases the lack of adjustment for folate intake status [4]. However, Venta et al. [14] suggested three possible mechanisms that may explain the increase in Hcy with increasing exercise intensity: increased free radical production [15], increases in methylated forms such as creatine and acetylcholine, and increases in the amino acid pool as a result of protein catabolism. The need for research in athletes who take part in different sports has been suggested to be important in order to account for the high prevalence of hyperchromocysteinemia [15]. To date, however, there have been no studies that evaluated plasma Hcy levels while taking into account nutrient intakes, training intensity and training time, and rate of perceived exertion (RPE). Moreover, the relationship between PA and Hcy has not been studied in team sports such as handball, in which intermittent activity alternates with periods of intense aerobic activity [24].

In the present study our aims were to evaluate macronutrient and folic acid nutritional status in high-performance athletes (handball players), and to determine the effect on these parameters of training and a nutritional intervention based on dietary supplementation with folic acid. We analyzed the data in the light of training load and plasma Hcy concentrations.

The results of the present study suggest that after the dietary and educational intervention, there were no significant changes in plasma concentrations of folic acid. However, we did note changes in plasma Hcy levels, despite the significant inverse correlation between the two values. Folic acid supplementation may have reduced cardiovascular risk during the NSTp in the handball players we studied.

In the present study, increased food intake as a result of nutritional education may have contributed to weight maintenance throughout the experimental period, which would avoid possible alterations in body weight as a result of poor dietary habits [1]. Regular PA is known to alter the requirements for certain micronutrients [1]. Folic acid intake in the athletes studied here (Table 2) was below the RDA except during Week 8, and was similar to the values reported by Rousseau et al. [12]. In this connection, a meta-analysis by Woolf and Manore [1] concluded that most studies which had analyzed folic acid intake based on a 3-day (72-h) recall period obtained values similar to those found in the present study. Supplementation with folic acid was implemented after an initial evaluation which showed the intake of this nutrient to be inadequate. The amount used in the dietary supplement was consistent with the theoretical basis described by McNully et al. [11], who suggested that doses of 0.2 to 0.4 mg folic acid per day may achieve maximal reductions in Hcy in healthy young people, whereas doses up to 0.8 mg folic acid per day would be needed to reduce Hcy in individuals with coronary artery disease. However, in the present study plasma Hcy concentration did not change despite the significant increase in folic acid intake.

Regular PA is known to reduce the risk of CVD [6, 12]. Handball, like other team sports such as soccer and field hockey, is considered an intermittent intensity sport on the basis of the aerobic energy pathways involved [31]. When we analyzed training load, we found a significant negative correlation between exercise training time at an intensity range of <60% RHR and plasma Hcy level (Figure 2). Rousseau et al. [12] reported that athletes who performed aerobic exercise had lower levels of Hcy. This finding is consistent with our results; moreover, our direct method for quantifying training load provided data that can be considered accurate and reliable. However, a potential limitation that should be taken into account is that the present study was done under actual training conditions, although it seems that a better study design would have been to (prospectively) control the volume and intensity of PA to keep them equal among participants.

Other authors reported different values for Hcy levels after exercise; the variations among different studies may reflect the use of indirect methods to quantify PA, the lack of nutritional studies and differences between studies in mean age of the participants [4, 31, 32].

It is worth noting that folic acid levels in plasma were near the lower limit of normality. Other authors found that a 5-mmol/l increase in plasma Hcy levels (>10 mmol/l) was associated with a 60% increase in the risk of coronary artery disease in men [8, 33]. McCully [10] noted that if the concentration of Hcy is between 8 and 12 mmol/l, improvements in the quality of the diet are needed to provide adequate vitamin intakes able to maintain Hcy at concentrations that can reduce the risk of coronary disease in adults. As described in the Results section, there was a significant negative correlation between plasma Hcy levels and plasma folic acid levels in Week 8. However, Hcy concentration increased despite dietary folic acid supplementation. This finding suggests that in contrast to the expected increase in plasma folic acid concentrations and decrease in Hcy, the opposite effect was likely attributable to training. In most participants in the present study, plasma levels of folic acid were near the lower limit of the reference values (4.2–19.l ng/ml), and after the intervention there was no significant change at the end of the supplementation period or at the end of the post-supplementation period. König et al. [5] showed that the increase in Hcy was dependent on the initial plasma level of folic acid as well as on training time. These authors attributed the increase in Hcy to increased methionine catabolism, which induced a greater influx of molecules with methyl groups as a result of high-intensity PA [4]. A study by Borrione et al. [15] analyzed team sports similar to handball but did not use dietary supplementation. They found Hcy levels that were much higher than those we found, and folic acid levels similar to those in the athletes we studied.

Our experimental approach was designed to evaluate training load, nutritional and biochemical indicators in an integrated manner to obtain accurate data in professional athletes during the sports season. Our method emphasized accurate data capture for both training load and dietary intakes. Variations in either of these factors can affect plasma levels of Hcy and folic acid, so it was important to avoid alterations that might compromise the data this study was designed to seek.

Our study appears to be the first to use careful controls for participants’ training load and nutritional and biochemical status before, during and after the professional sports season. Our results suggest that high-performance athletes such as handball players may require preventive dietary supplementation with folic acid to curtail the effects of a sharp increase in blood Hcy concentrations. This increase may be associated with a sudden increase in the risk of CVD as a result of the high training load accumulated in successive training sessions during the professional competition season.