Relationship between intake and plasma concentrations of vitamin B12 and folate in 873 adults with a physically active lifestyle: a cross-sectional study.

BACKGROUND: Vitamin B12 and folate function as co-factors in pathways used during physical activity. Physical activity may therefore increase vitamin requirements, leading to a risk of deficient plasma concentrations. We aimed to investigate the relationship between intake and plasma concentrations of vitamin B12 and folate in physically active adults, as well as identify other determinants of vitamin B12 and folate plasma concentrations. METHODS: The study population consisted of 873 adults (528 men and 345 women), aged 19-78 years, who participated in a 4-day walking event. The relationship between intake and plasma concentrations of vitamin B12 and folate was assessed using correlation and linear regression analyses. In addition, potential other determinants (sex, age, body mass index, energy intake and physical activity) of vitamin plasma concentrations were investigated. RESULTS: Significant positive correlations were observed between intake and plasma concentrations of vitamin B12 [Pearson's correlation coefficient = 0.15; 95% confidence interval (CI) = 0.08-0.21] and folate (Pearson's correlation coefficient = 0.18; 95% CI = 0.12-0.25). In addition to vitamin intake, sex, age and energy intake were also determinants of both vitamin B12 and folate plasma concentrations in multivariable regression models. CONCLUSIONS: The results suggest a positive association between intake and plasma concentrations for both vitamin B12 and folate in physically active people. By contrast to our hypothesis, physical activity was not a determinant of vitamin B12 and folate plasma concentrations. However, sex, age and energy intake were found to be determinants. Thus, when studying the relationship between intake and plasma concentrations of vitamin B12 or folate, these factors should be taken into account.

Ionized and Total Magnesium Levels Change during Repeated Exercise in Older Adults.

BACKGROUND: Magnesium is essential for health and performance. Sub-optimal levels have been reported for older persons. In addition, physical exercise is known to temporally decrease magnesium blood concentrations. OBJECTIVE: To investigate these observations in conjunction we assessed total (tMg) and ionized magnesium (iMg) concentrations in plasma and whole blood, respectively, during 4 consecutive days of exercise in very old vital adults. DESIGN: 68 participants (age 83.7±1.9 years) were monitored on 4 consecutive days at which they walked 30-40km (average ~8 hours) per day at a self-determined pace. Blood samples were collected one or two days prior to the start of exercise (baseline) and every walking day immediately post-exercise. Samples were analysed for tMg and iMg levels. RESULTS: Baseline tMg and iMg levels were 0.85±0.07 and 0.47±0.07 mmol/L, respectively. iMg decreased after the first walking day (-0.10±0.09 mmol/L, p<.001), increased after the second (+0.11±0.07 mmol/L, p<.001), was unchanged after the third and decreased on the final walking day, all compared to the previous day. tMg was only higher after the third walking day compared to the second walking day (p=.012). In 88% of the participants, iMg levels reached values considered to be sub-optimal at day 1, in 16% of the participants values were sub-optimal for tMg at day 2. CONCLUSION: Prolonged moderate intensity exercise caused acute effects on iMg levels in a degree comparable to that after a bout of intensive exercise. These effects were not associated with drop-out or health problems. After the second consecutive day of exercise, levels were returned to baseline values, suggesting rapid adaptation/resilience in this population.

Determinants of vitamin D status in physically active elderly in the Netherlands.

PURPOSE: Vitamin D deficiencies are common in elderly, which increases the risk for, e.g., bone fractures. Identification of determinants of vitamin D status may provide leads for specific deficiency prevention strategies. Although determinants of vitamin D status have been studied in various populations, this has not been examined in elderly that have a physically active lifestyle. METHODS: Vitamin D status of 450 physically active elderly who do not use vitamin D supplements was determined and information on possible determinants (demographic, dietary intake and physical activity) was collected around a prolonged four day walking event in July and analyzed in linear regression models. RESULTS: The average summertime serum 25(OH)D concentration was 88.8 ± 22.4 nmol/L. Only 2% of the participants had a 25(OH)D concentration below 50 nmol/L. Dietary intake of vitamin D was 4.0 ± 1.9 µg/day, and the participants spent 12.4 ± 8.6 h/week on outdoor activities. In the multivariate model, lower age (= - 0.48, 95% CI - 0.80 to - 0.16), lower BMI (= - 0.86, 95% CI - 1.62 to - 0.10), being a moderate to high drinker versus a non-drinker (= 7.97, 95% CI 0.43-15.51) and more outdoor physical activity (= 0.25, 95% CI 0.01-0.50) were significantly associated with higher 25(OH)D concentrations. CONCLUSIONS: In physically active elderly, vitamin D status was very high in summertime, with few deficiencies, suggesting that elderly with a physical active lifestyle might not necessarily need supplements during the summer period. Lower age, lower BMI, higher alcohol intake and more outdoor physical activity had a significant association with vitamin D status.

Fourteen residues of the U1 snRNP-specific U1A protein are required for homodimerization, cooperative RNA binding, and inhibition of polyadenylation.

It was previously shown that the human U1A protein, one of three U1 small nuclear ribonucleoprotein-specific proteins, autoregulates its own production by binding to and inhibiting the polyadenylation of its own pre-mRNA. The U1A autoregulatory complex requires two molecules of U1A protein to cooperatively bind a 50-nucleotide polyadenylation-inhibitory element (PIE) RNA located in the U1A 3' untranslated region. Based on both biochemical and nuclear magnetic resonance structural data, it was predicted that protein-protein interactions between the N-terminal regions (amino acids [aa] 1 to 115) of the two U1A proteins would form the basis for cooperative binding to PIE RNA and for inhibition of polyadenylation. In this study, we not only experimentally confirmed these predictions but discovered some unexpected features of how the U1A autoregulatory complex functions. We found that the U1A protein homodimerizes in the yeast two-hybrid system even when its ability to bind RNA is incapacitated. U1A dimerization requires two separate regions, both located in the N-terminal 115 residues. Using both coselection and gel mobility shift assays, U1A dimerization was also observed in vitro and found to depend on the same two regions that were found in vivo. Mutation of the second homodimerization region (aa 103 to 115) also resulted in loss of inhibition of polyadenylation and loss of cooperative binding of two U1A protein molecules to PIE RNA. This same mutation had no effect on the binding of one U1A protein molecule to PIE RNA. A peptide containing two copies of aa 103 to 115 is a potent inhibitor of polyadenylation. Based on these data, a model of the U1A autoregulatory complex is presented.

The U1 snRNP complex: an autoantigen in connective tissue diseases. An update.

The U1 small nuclear ribonucleoprotein (snRNP) particle consists of an RNA backbone and eleven associated proteins. Both the RNA and some of the proteins are immunogenic in patients suffering from systemic lupus erythematosus or mixed connective tissue disease. An overview is given of the U1 snRNP particle with respect to its structure and function as well as its autoantigenicity.

Nuclear accumulation of the U1 snRNP-specific protein C is due to diffusion and retention in the nucleus.

The U1 small nuclear ribonucleoprotein particle (snRNP) has an important function in the early formation of the spliceosome, the multicomponent complex in which pre-mRNA splicing takes place. The nuclear localization signals of two of the three U1 snRNP-specific proteins, U1-70K and U1A, have been mapped. Both proteins are transported actively to the nucleus. Here we show by microinjection of Xenopus laevis oocytes that the third U1 snRNP-specific protein, U1C, passively enters the nucleus. Furthermore, we show that in both X. laevis oocytes and cultured HeLa cells mutant U1C proteins that are not able to bind to the U1 snRNP do not accumulate in the nucleus, indicating that nuclear accumulation of U1C is due to incorporation of the protein into the U1 snRNP.