Background A variety of studies have noted seasonal variation in blood lipid levels. Although the mechanism for this phenomenon is not clear, such variation could result in larger numbers of people being diagnosed as having hypercholesterolemia during the winter. Methods We conducted a longitudinal study of seasonal variation in lipid levels in 517 healthy volunteers from a health maintenance organization serving central Massachusetts. Data collected during a 12-month period for each individual included baseline demographics and quarterly anthropometric, blood lipid, dietary, physical activity, light exposure, and behavioral information. Data were analyzed using sinusoidal regression modeling techniques. Results The average total cholesterol level was 222 mg/dL (5.75 mmol/L) in men and 213 mg/dL (5.52 mmol/L) in women. Amplitude of seasonal variation was 3.9 mg/dL (0.10 mmol/L) in men, with a peak in December, and 5.4 mg/dL (0.14 mmol/L) in women, with a peak in January. Seasonal amplitude was greater in hypercholesterolemic participants. Seasonal changes in plasma volume explained a substantial proportion of the observed variation. Overall, 22% more participants had total cholesterol levels of 240 mg/dL or greater (≥6.22 mmol/L) in the winter than in the summer. Conclusions This study confirms seasonal variation in blood lipid levels and suggests greater amplitude in seasonal variability in women and hypercholesterolemic individuals, with changes in plasma volume accounting for much of the variation. A relative plasma hypervolemia during the summer seems to be linked to increases in temperature and/or physical activity. These findings have implications for lipid screening guidelines. Further research is needed to better understand the effects of a relative winter hemoconcentration.

https://jamanetwork.com/journals/jamainternalmedicine/articlepdf/216973/ioi30014.pdf

Seasonal variation in serum cholesterol levels: treatment implications and possible mechanisms.

Background—A suboptimal haematological status has often been recorded in athletes involved in intensive physical activity. There have even been reports of "sports anaemia" associated with intensive physical exercise. However, studies on the effect of different types of exercise practiced over a long period of time on the red blood cell variables in pubescent athletes are very few. 

Aim—To assess the basic red blood cell variables in highly trained pubescent athletes from different sports and to compare the results with those for a control untrained group. Sex related differences in these variables were also assessed. 

Methods—876 highly trained athletes (559 boys and 317 girls) were included in the study. Their mean (SEM) age, weight, and duration of training were: 14.01 (0.06) years, 56.24 (0.52) kg, and 3.52 (0.07) years respectively. The control group consisted of 357 untrained subjects (171 boys and 186 girls) with mean (SEM) age and weight of 14.58 (0.09) years and 57.75 (0.67) kg. The group of athletes was divided into seven subgroups according to the sport practiced: athletics (105), swimming (107), rowing (230), wrestling (225), weight lifting (47), various team sports (92), and other sports (67). Venous blood samples were drawn from the cubital vein, and the red blood cell count, packed cell volume, haemoglobin concentration, and mean corpuscular volume were measured. Statistical indices were computed for each group and for each variable, and analysis of variance factorial analysis was performed to evaluate the statistical significance of the differences detected. 

Results—The highly trained group was found to have lower red blood cell count, packed cell volume, and haemoglobin concentration (p<0.001) than the control untrained group (4.61 (0.01) x 1012/1 v 4.75 (0.02) x 1012/l, 0.389 (0.001) v 0.404 (0.002) l/l, and 133.01 (0.38) v 139.9 (0.62) g/l respectively). These variables were lower for the boys of the trained group than for the boys of the control group (p<0.001), and similarly for the girls (p<0.001). The lowest red blood cell count, packed cell volume, and haemoglobin concentration were measured in blood samples from the boys of the swimming subgroup (4.54 (0.06) x 1012/l, 0.386 (0.006) l/l, and 129.38 (1.80) g/1 respectively) and the rowing subgroup (4.66 (0.03) x 1012/l, 0.400 (0.003) l/l, and 136.21 (0.94) respectively). The same distribution was found for the girls: lowest in the rowing subgroup (4.32 (0.04) x 1012/1, 0.314 (0.003) l/l, and 124.27 (0.93) g/1) and the swimming subgroup (4.40 (0.05) x 1012/l, 0.375 (0.005) l/l, and 125.90 (1.30) g/1). No differences were found in the mean corpuscular volume. 

Conclusions—Continuous (more than one year) high intensity sports training (twice a day/five days a week) results in a decrease in the basic red blood cell variables in pubescent boys and girls, this being most pronounced in the submaximal sports. 

Key Words: erythrocytes; haemoglobin; packed cell volume; mean corpuscular volume; pubescence; training

https://bjsm.bmj.com/content/bjsports/34/3/200.full.pdf

Red blood cell variables in highly trained pubescent athletes: a comparative analysis.

The effects of magnesium supplementation on blood parameters were studied during a period of 4 wk in adult tae-kwon-do athletes at rest and exhaustion. Thirty healthy subjects of ages ranging in age from 18 to 22 yr were included in the study. The subjects were separated into three groups, as follows: Group 1 consisted of subjects who did not train receiving 10 mg/kg/d magnesium. Group 2 included subjects equally supplemented with magnesium and exercising 90-120 min/d for 5 d/wk. Group 3 were subject to the same exercise regime but did not receive magnesium supplements. The leukocyte count (WBC) was significantly higher in groups 1 and 2 than in the subjects who did not receive any supplements (p < 0.05). There were no significant differences in the WBC of the two groups under magnesium supplementation. The erythrocyte, hemoglobin, and trombocyte levels were significantly increased in all groups (p < 0.05), but the hematocrit levels did not show any differences between the groups although they were increased after supplementation and exercise. These results suggest that magnesium supplementation positively influences the performance of training athletes by increasing erythrocyte and hemoglobin levels.

Effects of magnesium supplementation on blood parameters of athletes at rest and after exercise.

Classically, cold induced plasma volume reduction is explained by an increased diuresis which is generated by an inhibition of antidiuretic hormone release. However, most of the haemoconcentration appears to be reversible during rewarming. This observation weakens the former statement. The aim of this study was to clarify the mechanisms involved in the reversal of the cold induced haemoconcentration. Six young males, resting in a dorsal reclining position, were exposed successively to a thermoneutral environment (30 min), a cold environment (1 degrees C; cold) or thermoneutrality (control) for 120 min, and during a 60-min recovery period in thermoneutral conditions. During cold stress, a reduction of 15% (i.e. 510 ml) of the plasma volume was observed, and osmolality was unchanged. After the 60-min recovery under thermoneutral conditions, plasma volume variation between the Cold and the Control experiments was reduced and reached 3% (i.e. 100 ml). This volume equalled the increased amount of urine production observed during the cold stress experiment. Haemoconcentration cannot be explained by increased urinary water loss (+/- 100 ml) alone. Therefore a transient shift of plasma water from vascular to interstitial spaces, due to an increase of blood pressure, could be involved in the reduction of plasma volume.

Reversal of cold induced haemoconcentration.

The purpose of this study is to explore possible potential implications of cold air in cardiovascular disease (CVD) risk in rats Healthy Wistar rats were exposed to artificial cold air under laboratory conditions, and their systolic blood pressure, heart rate, vasoconstriction, CVD risk factors, and myocardial damage indicators after cold air exposure were determined and evaluated Systolic blood pressure, whole blood viscosity, and plasma level of norepinephrine, angiotensinⅡ, low density lipoprotein, total cholesterol, and fibrinogen in treatment groups increased significantly compared with control groups No significant variations were found in plasma Mb and cTnT and myocardial tissue between the treatment and control groups Results indicate that: (1) higher levels of SBP, WBV and LDL/HDL, total cholesterol (TC), and FG in blood may indicate higher CVD risks during cold air exposure; (2) cold air may exert continuous impacts on SBP and other CVD risk factors

https://www.mdpi.com/1660-4601/9/7/2312/pdf?y=1

Effects of cold air on cardiovascular disease risk factors in rat.

The affect of negative thermal stress on hematological variables at rest, and during submaximal (sub ex) and maximal exercise (max ex) were observed for young males who volunteered in two experimental sessions, performed in cold (0 degree C) and in normal room temperature (20 degrees C). At rest, hematological variables such as RBC and derivates Hb and Hct were significantly increased (P less than 0.05) during cold stress exposure, while plasma volume decreased. The findings of this study suggest that the major factor inducing hypovolemia during low thermal stress can be imputed to local plasma water-shift mechanisms and especially to a transient shift of plasma water from intra- to extravascular compartments. Rest values for WBC and platelets (Pla) were also slightly increased during cold stress exposure. However this increase can partly be related to hemoconcentration but also to the cold induced hyperventilation activating the lung circulation. Maximal exhaustive exercise induced, in both experimental temperatures, significant (P less than 0.05) increments of RBC, Hb, Hct, and WBC while plasma volume decreased. However, Pla increase was less marked. On the other hand, cold stress raised slightly the observed variations of the different hematological variables. Submaximal exercise induced a similar, though non-significant, pattern for the different hematological variables in both experimental conditions. Observed plasma volume (delta PV%) reduction appears during exercise. However cold stress induced resting plasma volume variations that are transferred at every exercise level. Neither exercise nor cold inducement significantly modified the hematological indices (MCH, MCV, MCHC). In conclusion hematological variables are affected by cold stress exposure, even when subjects perform a physical activity.

Hematological variations at rest and during maximal and submaximal exercise in a cold (0°C) environment

The purpose of this study was to determine the effects of cold stress on routine hematologic parameters when subjects are submitted on long-lasting exercise. Eight male subjects, aged 22.7 +/- 1.3 years with a peak oxygen consumption of 54.3 +/- 5.2 mL/kg/min performed, respectively at 20 degrees C and 0 degrees C, a two-hour submaximal cyclergometry at an intensity of 40% of that performed during a previous exhaustive test. A 21-gauge catheter was inserted into an ante cubital vein for collection of the blood samples. Platelets and WBC count was significantly (p less than 0.05) increased during exercise in both 20 degrees C and 0 degrees C environmental temperatures. A slight but not statistically significant increase of RBC, Hb and Hct and a plasma concentration during cold exposure was observed. Indices are unchanged in both experiments. The findings of this study suggest that physical exercise is a major factor inducing hypervolemia and that low thermal environment does not appear to be an effective factor influencing hematologic variables during exercise.

[Hematological variations with submaximal long-term physical exercise].

Variations hematologiques à l'exercice physique sous maximal de longue durée.

Cette etude a pour but d'etudier les variations physiologiques et metaboliques tant au repos, qu'au cours d'efforts physiques de longue duree (2h) a 40% de la puissance maximale et d'efforts exhaustifs dans des conditions d'hypothermie ambiante (0‡C) en comparaison de valeurs recueillies en conditions thermiques neutres (20‡C). L'ensemble des epreuves furent executees en chambre climatique par: d'une part 11 sujets mâles pour l'effort exhaustif et d'autre part 8 sujets mâles pour l'exercice sous-maximal. Nous avons observe une legere bradycardie a 0‡C pour nos deux groupes a la fin de l'effort. La VO2 et la ventilation pulmonaire sont plus elevees a 0‡C lors de l'effort maximal, nous observons toutefois le phenomene inverse lors de l'exercice sousmaximal. Les concentrations plasmatiques en acide lactique sons moins elevees et les bicarbonates plus eleves en ambiance thermique froide pour les deux conditions experimentales. Le pH et la temperature rectale demeurent stables. Le RQ ne presente pas de differences significatives a la fin de chacun des deux efforts a 20‡C et 0‡C.

Variations cardio-respiratoires et metaboliques à l'effort sous-maximal (P=40% Pmax) et maximal (Vita Max) en conditions thermiques froide (0‡C) et neutre (20‡C)

Die physiologische Adaptation von Menschen an Kalteeinwirkung ist uberwiegend im Sinne einer Akklimatisation an die Umgebung untersucht worden. In dieser Studie soll jedoch wahrend und nach einer Arbeit untersucht werden, ob es Differenzen bezuglich der kardio-respiratorischen Leistung sowie metabolischer Parameter gibt zwischen Mannern, die an Kalteeinwirkung gewohnt sind und solchen, die dieses nicht sind. Um dieses Ziel zu erreichen, wurden die Untersuchungen simultan von zwei unterschiedlichen Arbeitsgruppen und zwar in Quebec und Brussel, durchgefuhrt. Als erstes Ergebnis dieser Studie liegen die Resultate der nicht an die Kalte gewohnten Probanden vor, die die maximale fahrradergometrische Leistung sowohl bei 20 °C als auch bei 0 °C erbringen musten. Wahrend dieser kurzen Ausbelastungsphase lies sich — wie aus der Literatur zu erwarten — eine Bradykardie unter Ruhebedingungen sowie wahrend und nach der kurzen, aber erschopfenden Leistung nachweisen. Die \( \frac{.}{V}{O_2} \) war wahrend der Arbeit und danach bei einer Temperatur von 0 °C signifikant (p ≤ 0,05) erhoht. Die Laktatkonzentration war wahrend aller Meszeiten niedriger wahrend des Tests bei 0 °C und erreichte einen statistisch signifikanten Unterschied (p ≤ 0,05) in der Erholungsphase.

R. Leclercq

Papers

Hematological variations at rest and during maximal and submaximal exercise in a cold (0°C) environment

[Hematological variations with submaximal long-term physical exercise].

Variations hematologiques à l'exercice physique sous maximal de longue durée.

Variations cardio-respiratoires et metaboliques à l'effort sous-maximal (P=40% Pmax) et maximal (Vita Max) en conditions thermiques froide (0‡C) et neutre (20‡C)

Zur Kälteadaptation während körperlicher Leistung — Vorläufige Ergebnisse