Micronutrients Vitamins Research Articles

Organic food: nutritious food or food for thought? A review of the evidence

Apparently, one of the primary reasons for purchasing organic food is the perception that it is more nutritious than conventional food. Given the increasing interest towards organic food products, it is imperative to review the existing literature concerning the nutritional value of the produce, and to determine to what extent are consumer expectations met. There are only few well-controlled studies that are capable of making a valid comparison and, therefore, compilation of the results is difficult and generalisation of the conclusions should be made with caution. In spite of these limitations, however, some differences can be identified. Although there is little evidence that organic and conventional foods differ in respect to the concentrations of the various micronutrients (vitamins, minerals and trace elements), there seems to be a slight trend towards higher ascorbic acid content in organically grown leafy vegetables and potatoes. There is also a trend towards lower protein concentration but of higher quality in some organic vegetables and cereal crops. With respect to the rest of the nutrients and the other food groups, existing evidence is inadequate to allow for valid conclusions. Finally, animal feeding experiments indicate that animal health and reproductive performance are slightly improved when they are organically fed. A similar finding has not yet been identified in humans. Several important directions can be highlighted for future research; it seems, however, that despite any differences, a well-balanced diet can equally improve health regardless of its organic or conventional origin.

Dietary Antioxidants, Supplements, and Risk of Epithelial Ovarian Cancer

Several studies of dietary and serum antioxidant micronutrients (vitamins A, C, and E and β-carotene) suggest that higher levels may be protective for ovarian cancer. None of these has examined supplements. We used a food frequency questionnaire and additional questions on supplements to study 168 histologically confirmed epithelial ovarian cancer cases, 159 community controls, and 92 hospital-based controls. Antioxidant consumption from diet or supplements was calculated in milligrams or international units per day. In multivariate analyses using only community controls, the highest levels of intake of vitamins C and E from supplements were protective: odds ratio (OR) = 0.40 [95% confidence interval (CI) = 0.21-0.78] and OR = 0.33 (95% CI = 0.18-0.60), respectively. Consumption of antioxidants from diet was unrelated to risk. In analyses combining antioxidant intake from diet and supplements, vitamins C (>363 mg/day) and E (>75 mg/day) were associated with reduced risks: OR = 0.45 (95% CI = 0.22-0.91) and OR = 0.44 (95% CI = 0.21-0.94), respectively. Results were similar, with some attenuation toward the null, in analyses combining both control groups. The levels of vitamins C and E associated with the protective effect were well above the current US Recommended Dietary Allowances. These findings support the hypothesis that antioxidant vitamins C and E from supplements are related to a reduced risk of ovarian cancer.

The Influence of Factory and Region on the Composition of South African Cheddar and Gouda Cheese

The aim of this study was to determine the nutrient composition of cheddar and gouda cheese as consumed by the public and to investigate whether there were any influences of the different factories or regions on the composition of cheddar and gouda cheese. It was decided, in collaboration with biometricians to take 10 samples per factory, for the different cheeses. The seven factories sampled represent nearly 90% of the South African cheddar and gouda market. A canonical variate analysis (CVA) on the cheddar cheese results showed that CV1 and CV2 accounted for 87% of the total variation in the composition of cheddar cheese, with locality or region influencing the nutrient composition. The micronutrients vitamin B2, zinc, manganese, potassium, retinol, magnesium and calcium were mainly responsible for the variations in the composition of cheddar cheese. A CVA on gouda cheese showed that CV1 and CV2 accounted for 85% of the total variation in the composition of gouda cheese. The micronutrients vitamin B1, vitamin E, manganese, zinc, β -carotene, retinol and phosphorus were mainly responsible for the variations in the composition of gouda cheese. Locality or region differentiated the data so clearly that the factories were grouped into regions namely the Eastern Cape, Western Cape and North West Province.

Lipases and Carboxylesterases: Possible Roles in the Hepatic Utilization of Vitamin A

The formation and hydrolysis of retinyl esters are key processes in the metabolism of the fat-soluble micronutrient vitamin A. Long-chain acyl esters of retinol are the major chemical form of vitamin A (retinoid) stored in the body. Although retinyl esters are found in a variety of tissues and cell types, most of the total body retinoid is accounted for by the retinyl esters stored in the liver. Thus, these esters represent the major endogenous source of retinoid that can be delivered to peripheral tissues for conversion to biologically active forms. This paper summarizes the current state of our knowledge about the identity, function and regulation of the hepatic enzymes that are potentially involved in catalyzing the hydrolysis of retinyl esters. These enzymes include several known and characterized lipases and carboxylesterases.

Nonpharmacologic therapy of osteoarthritis.

Studies of the nonpharmacologic treatment of osteoarthritis (OA) have fallen behind that of pharmacologic therapy for a variety of reasons. The design of studies that involve a therapist-delivered physical intervention presents several problems with respect to patient and observer blinding, the beneficial effect of therapist contact alone, and separation of the effects of individual components of the "package" of delivered care. Important developments in the design and reporting of OA trials are discussed. Recent studies have demonstrated the modest but definite benefits of exercise therapy for OA of the knee, delivered either in hospital, primary care, or community settings. The reduction in pain and disability through an arthritis self-management group education program may extend to at least 1 year. Recent data that low intake of micronutrients (vitamins C, E, and D, and beta-carotene) may adversely influence the progression of knee OA and the incidence of hip OA suggest potential avenues for primary and secondary prevention of large joint OA.

Lipases and carboxylesterases: possible roles in the hepatic metabolism of retinol.

The formation of hydrolysis of retinyl esters are key processes in the metabolism of the fat-soluble micronutrient vitamin A. Long-chain acyl esters of retinol are the major chemical form of vitamin A (retinoid) stored in the body. Retinyl esters are found in a variety of tissues and cell types, but most of the total body retinoid is accounted for by the retinyl esters stored in the liver. Thus, these esters represent the major endogenous source of retinoid that can be delivered to peripheral tissues for conversion to biologically active forms. This review summarizes current knowledge about the identity, function, and regulation of the hepatic enzymes potentially involved in catalyzing the hydrolysis of retinyl esters. These enzymes include several known and characterized lipases and carboxylesterases. Although there is accumulating evidence that these enzymes function as retinyl ester hydrolases in vitro, it is not clear which play important physiological roles in hepatic retinyl ester metabolism.

Simultaneous determination of serum retinol, tocopherols, and carotenoids by HPLC.

Epidemiological studies have confirmed that dietary supplementation with vitamin E significantly inhibits oxidation of low-density lipoproteins () and reduces the risk of atherosclerosis () and coronary heart disease (). Retinol and β-carotene (β-caro) are important micronutrient vitamins in reducing the risk of age-related macular degeneration () and cancer (). The simultaneous determination of retinol, tocopherols, and carotenoids by high-pressure liquid chromatography (HPLC) using ultraviolet-visible absorbance (UV-VIS) detection has become the method of choice for investigators interested in determining fat-soluble vitamin levels in health and disease (). This method achieves the desired separation and provides quantitation of numerous fat-soluble vitamins in biological specimens (). Furthermore, the performance characteristics of the method have been extensively studied by the National Institute of Standards and Technology (NIST/NCI Micronutrients Measurement Quality Assurance Program, Chemistry B208, Gaithersburg, MD), which now supplies both quality-control material and offers proficiency testing for multiple analytes, as well as workshops on HPLC analysis of these analytes.

Cross-Sectional Study with Multiple Measurements of Biological Markers for Assessing Stomach Cancer Risks at the Population Level

A cross-sectional study to determine correlations between measurable biologic markers and mortality from stomach cancer was performed in various areas of Japan. Blood and urine were collected from randomly selected 40- to 49-year-old men and their spouses in four areas with different rates of mortality from stomach cancer. The samples were analyzed for levels of the micronutrients vitamins A, C, and E, beta-carotene, and lycopene in plasma and for levels of NaCl, nitrate, and N-nitrosamino acids (N-nitrosoproline, N-nitrosothioproline [NTPRO] and N-nitrosomethylthioproline [NMTPRO]) in 24-hr urine. A significant, strong correlation was found between the amount of salt excreted in urine and stomach cancer mortality in both men and women. Although the amounts of nitrate and of the three N-nitrosamino acids in 24-hr urine were not correlated with stomach cancer rates, the low excretion levels of NTPRO and NMTPRO in the lowest risk area for stomach cancer were noteworthy, regardless of the high level of nitrate excretion in the same area. This suggests a lesser degree of endogenous nitrosation in the body. No protective effect of micronutrients was observed in this correlation study; there was, however, a negative correlation between plasma lycopene level and stomach cancer mortality. Salt intake was thus confirmed to play an important role in the development of stomach cancer and is likely to be a rate-regulating factor in Japanese populations. N-Nitrosamino acids and lycopene may also be related to stomach cancer mortality.

Cross-sectional study with multiple measurements of biological markers for assessing stomach cancer risks at the population level.

A cross-sectional study to determine correlations between measurable biologic markers and mortality from stomach cancer was performed in various areas of Japan. Blood and urine were collected from randomly selected 40- to 49-year-old men and their spouses in four areas with different rates of mortality from stomach cancer. The samples were analyzed for levels of the micronutrients vitamins A, C, and E, beta-carotene, and lycopene in plasma and for levels of NaCl, nitrate, and N-nitrosamino acids (N-nitrosoproline, N-nitrosothioproline [NTPRO] and N-nitrosomethylthioproline [NMTPRO]) in 24-hr urine. A significant, strong correlation was found between the amount of salt excreted in urine and stomach cancer mortality in both men and women. Although the amounts of nitrate and of the three N-nitrosamino acids in 24-hr urine were not correlated with stomach cancer rates, the low excretion levels of NTPRO and NMTPRO in the lowest risk area for stomach cancer were noteworthy, regardless of the high level of nitrate excretion in the same area. This suggests a lesser degree of endogenous nitrosation in the body. No protective effect of micronutrients was observed in this correlation study; there was, however, a negative correlation between plasma lycopene level and stomach cancer mortality. Salt intake was thus confirmed to play an important role in the development of stomach cancer and is likely to be a rate-regulating factor in Japanese populations. N-Nitrosamino acids and lycopene may also be related to stomach cancer mortality.

Nutrition and esophageal cancer

Several case control studies in esophageal cancer employing a food-frequency dietary questionnaire suggested a fairly uniform dietary pattern which could be implicated in the causation of the disease. Although various micronutrients (vitamins and trace elements) have also been found to have either a positive or negative association, findings were more clear-cut for the different food items contributing the micronutrients than for the specific micronutrients themselves. The difficulties encountered in dietary interviews in case control studies are discussed. Nutritional supplementation has a theoretical rationale, but clinical experience with randomized trials did not support the same.

Influence of life-prolonging dietary restriction on intestinal vitamin A absorption in mice

We studied influences of life prolonging dietary restriction on the absorptive capacity of the small intestine for the lipid micronutrient, Vitamin A. Using a well established intestinal perfusion technique, we measured the vitamin absorption rates in vivo in male mice fed regular laboratory chow (LC) ad lib, female mice on 95 kcal/week of a semipurified diet (designated “N” for normally fed), and female mice restricted to a 55 kcal/wk diet fed four days per week (R). The absorption rate of vitamin A was the lowest in LC mice and highest in R mice. Both at 6 and 26 months of age, R mice absorbed significantly more vitamin A than did the N mice. For example, at 6 months, R mice absorbed 10696 pmol/100 cm/hr while N mice absorbed only 7986 pmol/100 cm/hr (p<.01). Thus, dietary restriction increased the absorptive capacity of the small intestine for the lipid micronutrient vitamin A. The mechanisms responsible remain unknown, but could involve changes in the unstirred water layer resistance or in the lipid cell membrane of the enterocytes.