Henk van den Berg

Vitamins and cancer

The prospect that high intake of certain vitamins may confer protection against cancer has drawn substantial attention during the last decades. This paper gives a concise update of the role of a number of promising vitamins in prevention of cancer. Vitamin A and its analogues have an important role in cellular processes related to carcinogenesis. However, blood vitamin A levels are under strict control and a high intake of preformed vitamin A does not seem to be relevant for cancer prevention. The antioxidant vitamins C and E and β-carotene may also have other biological activities than free radical trapping that relate to their cancer preventive properties. Mechanisms include immune stimulation, inhibition of nitrosamine formation, enhancement of cell communication and an influence on metabolic activation of carcinogens. Epidemiological data for the antioxidant vitamins are promising, but cannot rule out that another factor or combination of factors in fruits and vegetables might be responsible for a protective effect. The B vitamin folic acid is one of these potential factors that is currently thought to have an influence on DNA methylation and thus on proto-oncogene expression. Folic acid seems to be promising and deserves further study. Vitamin D might be relevant in colon cancer development due to its close links with calcium metabolism that might influence cell proliferation. Overall, results are promising, but the first human intervention trials on (antioxidant) vitamins and human cancer have yielded somewhat disappointing results. At this moment the data seem insufficient to make recommendations for vitamin supplementation to prevent cancer. The results are certainly in line with the advice that a diet rich in fruits and vegetables will help reduce cancer risk.

Energy and fat compensation during long-term consumption of reduced fat products.

The objective of this study was to investigate the behavioral response to the long term realistic consumption of reduced fat products. During six months, a control group of 103 subjects had free access to about 45 commercially available full-fat products, and a reduced-fat group of 117 subjects had access to the reduced fat equivalents. These experimental products covered about 37% of total energy intake in the control group and 30% of energy intake in the reduced fat group. Other non-experimental food products were bought in regular shops. The results showed that, compared to a baseline measurement before the start of the study, energy intake increased from 10.4 MJ/day to 11.2 MJ/d in the control group, whereas it remained constant at 10.2 MJ/d in the reduced fat group. Fat intake in the control group increased from 99 g/d (35.6en%) to 123g/d (40.6en%), whereas fat intake in the reduced fat group decreased from 95 g/d (34.en%) to 90 g/d (32.7en%). The energy and fat intake from experimental products was lower in the reduced fat group (3.1 MJ/d, 37 g fat/d) than in the control group (4.2 MJ/d, 71 g fat/d). There was some compensatory response in the consumption of experimental products: the ingested amount of experimental products was about 10% higher in the reduced fat group (447 g/d) than in the control group (399 g/d)[t = 2.6; p < 0.01]. There was no compensatory response in the consumption of non-experimental products. Both the control and reduced fat group consumed about 7.1 MJ/d and 53 g fat/d from non-experimental products. It is concluded that long term consumption of reduced fat products leads to a lower energy and fat intake, compared to the consumption of full-fat products.

Effect of Aging on Vitamin B6 Status and Metabolism

The age group of 85 years and over is currently the fastest-growing age cohort in the United States, and in most Western countries the proportion of elderly people (>65 yr) is expected to increase in the next decades to about 20% of the total population. This may explain the growing interest in the relationship between aging and nutrition. First of all, reliable, quantitative data are needed on nutrient requirements for the different age groups, especially for the elderly. Besides, there is a strong interest in the role of nutrition as one of the lifestyle and environmental factors that can modify the aging process and may play a role in the cause as well as in the prevention of age-related diseases. Vitamin B, is an essential nutrient involved in protein metabolism, neurotransmitter synthesis, and steroid hormone action. It is uncertain whether elderly and younger adults differ in vitamin B, requirement as a result of age-related changes in vitamin B, metabolism.

Pyridoxal-5′-phosphate and pyridoxal biokinetics in aging Wistar rats

Biokinetic parameters of plasma pyridoxal-5-phosphate (PLP) and pyridoxal (PL) disposition were studied in male Wistar rats aged 8 and 27 months kept from weaning on a purified diet containing 250 g casein and 6 mg pyridoxine.HCl per kg. Baseline plasma PLP concentration was lower in the older animals (514 +/- 56 nmol/L for young and 317 +/- 124 nmol/L for old animals), whereas baseline plasma PL concentration did not differ between age groups (average 235 nmol/L for both young and old animals). We hypothesized lower baseline plasma PLP in the older animals was caused by an increased PLP elimination rate, a decreased PLP synthesis rate, or a combination of these processes. Observations from earlier in vitro experiments suggest age-related changes occur in vitamin B-6 metabolizing enzyme activities. In the in vivo experiments described here no age-related difference in plasma PLP elimination rate nor in plasma PLP synthesis rate was observed to explain the observed decrease in plasma PLP concentration with age.