II. Protective Food Components

In the realm of the ‘good stuff’, the first question is whether or not organics have higher levels of important nutrients. The answer is by no means definite but research of varying quality exists and early conclusions can be drawn. Question 2 – whether these variations have any significant impact on human nutrition – is still wide open.  As mentioned previously, few studies have attempted to measure health effects from the potentially beneficial chemical components of organic produce. The one consistent conclusion that can be found in the literature is a call for improved study and research into the topic.

Primary Nutrients & Heavy Metals

A metanalysis of 41 studies from 1946 to 2001 found statistically significant differences in levels of vitamin C, iron, magnesium and phosphorous in organic versus conventionally produced vegetables. Mean percentage difference was +27.0% in vitamin C, +21.1% in iron, +29.3% in magnesium and +13.6% in phosphorous. The metanalysis uncovered other interesting but nonsignificant trends in minerals and heavy metals: Each of 21 nutritionally important minerals were present at higher levels in organic vegetables than conventional. Examples include chromium (86% higher), iodine (50%), and calcium (30%). Among the studies sampled, lower amounts of heavy metals were found in organic vegetables more often than in conventional. Organic crop had less lead in 7 comparisons but more lead in 5 comparisons. Similar results were 6 vs. 5 for cadmium, 3 vs. 2 for mercury, and 4 vs. 1 for aluminum (Worthington 2001).

One of the flaws with metanalysis in this area is that many of the comparative studies have different design and there are inconsistencies in metrics, calling into question comparability of results between studies. Indeed, in its 2001 review of the evidence, the Soil Association of England rejected 70 of 99 studies comparing nutritional quality between organic and conventional foods. In their words, “[The studies] often compare nutrient contents inappropriately on a dry weight basis, do not actually compare crops produced using recognised organic and non-organic farming practices, or compare the correct farming methods but for too short a period to properly represent certified organic farming which must go through at least a two year conversion period to improve the soil.” Looking at the remaining studies, the review concluded that organic crops seemed higher in vitamin C, some essential minerals (calcium, magnesium, iron and chromium), and phytonutrients (lycopene in tomatoes, polyphenols in potatoes, flavonols in apples, and resveratrol in red wine) (Heaton 2001).

Another review, published in 2003, concluded there was not, as yet, evidence to support an overall conclusion that organic food has higher nutrient value. The authors add a different argument with regard to the body of literature, “Where differences have shown up, they do not consistently give the nutritional edge to either type of food, probably because the variability within a given crop is greater than the variability between one cropping system and another.” That said, this review does supports the following conclusions: organics generally have lower protein density but the protein is of higher quality and organically grown leafy vegetables and potatoes seems appear to hold higher ascorbic acid (vitamin C) content (Magkos et al. 2003).

Measuring the levels of particular nutrients in produce does not tell us whether or not these nutrients have a differential effect on human health. While there is a scarcity of data looking at impact on human health, particularly in the form of controlled interventional trials, older research looking at effects of organic feed on animals does exist (Bourn et al. 2002; Williams 2002). Studies on rats and rabbits show results such as larger litters in the second and third generations of animal raised on organic feed, potentially indicating increased fertility from organic diet (Staiger 1988; Velimirov et al. 1992). Decreased susceptibility to infections has been detected in rabbit populations given organic feed, as well as decreased mortality in newborn rabbits (Staiger 1988; Vogtmann 1988). Mechanisms for these results are unclear and several other studies exist that show no benefit from organic feed (Bourn & Prescott 2002). [See Williams 2002 for a thorough and concise summary of the rodent and rabbit data].

In humans, one study in Denmark found lower sperm counts in conventional farmers as compared to organic farmers (Jensen et al. 1996). [See Bourn & Prescott 2002 for a review of the small body of work on human sperm quality and organic food consumption.] Other observational studies have found no effects. Summarizing the research on humans, British researcher C. Williams made the following point: “Lack of relevant dietary data, heterogeneity in the study populations and limited information on growing conditions of the foods used means that much of this early data cannot be scrutinised according to current scientific criteria. For this reason no valuable inferences or interpretations can be derived from these studies” (Jensen et al. 1996).

Phenolic / Antioxidant Compounds
 In the last few years, there has been an uptick in research investigating antioxidant levels in fruits and vegetables grown organically. Antioxidant or phenolic compounds are believed to play a role in plant immunity by acting as a chemical barrier to pathogens when they invade. Evidence that certain phenolics are found in higher concentrations in organically grown fruits and vegetables is accumulating. The absence of synthetic pesticides appears to allow higher rates of phytopathogenic infiltration in the growing plants, and in turn, higher levels of phenolics in defense. In addition to their presumptive beneficial health effect on humans, antioxidants contribute to the shelf life of produce, protecting against oxidative degeneration (Carbonaro et al. 2002).
 [Researchers at UC Davis founnd higher levels of total phenolics in marionberry, strawberry and corn. They also looked at the effects of postharvest processing (freezing, freeze-drying, and air-drying) and found that freeze-drying preserved phenolic content better. The study is often cited in the literature.] (Asami et al. 2003)

In a study of peaches and pears grown in Italy, various polyphenols were between 10% and 36% higher (P < 0.05) in the organic batch compared to the conventional batch. Organic peaches had 29.0±1.2  mg tannic acid/100 g fresh weight (a measure of total polyphenols) compared to 21.3±1.6 mg tannic acid/100 g fresh weight in conventional peaches (P < 0.01). Organic pears had 64.5±1.5  mg tannic acid/100 g fresh weight compared to 58.4±2.0 mg tannic acid/100 g fresh weight in conventional pears (P < 0.05).  The samples were taken from the same farm on the same day and the organic fruits were certified in accordance with EC and Italian organic certifications (Carbonaro et al. 2002).
Salicylic acid (aspirin) can be found in plants as part of their response to pathogenic invasion. Aspirin has been established as a blood thinner for heart disease and has an anti-inflammatory effect that may reduce risk of atherosclerosis and colorectal cancer. In 2001, researchers in Scotland investigated whether soups made of organically grown produce contained higher levels of salicylic acid.  Previously, the same group had found higher salicylic acid blood serum levels in vegetarian versus non-vegetarian population, which provides a degree of evidence that dietary aspirin intake is in fact reflected in blood serum levels. The salicylic acid serum level in the vegetarian group that they studied (Buddhist monks, n=37) was 0.11 μmol/L compared to 0.07 μmol/L in a non-vegetaria group recruited from the community (n=39), with a statistically significant difference of 0.05 μmol/L (95% CI, 0.03 to 0.08; p < 0.0001). To provide a point of reference, this was about 100x lower than the average blood serum level of a people taking daily doses of aspirin tablets (n=14) for prophylactic purposes (Blacklock et al. 2001).

The same researchers went on to measure salicylic acid levels in a variety of organic and conventional vegetable soups found at local retailers. The soups included varieties such as tomato, tomato and basil, carrot and coriander, and vegetable soup. Organic soups (n=11) were found to contain a median level of 117 ng/g of salicylic acid compared to 20 ng/g in non-organic soups (n=24) (Baxter et al. 2001). Other factors such as processing and handling by the manufacturer could have been at work and one of the problems of the retail market studies is that it is difficult to know exactly what organic methods were used in growing the vegetables. That said, the research is significant for showing a meaningful difference in organic versus conventional produce at the retail level where most people buy their food (Magkos et al. 2006).

[Danish researchers investigated flavanoid levels in the urinary output of human subjects in an interventional trial looking at the effect of 22 days of organic versus conventional diet and found no meaningful difference. They went on to measure blood plasma of the subjects and found evidence of increased protein oxidation and a decreased total plasma in the organically fed group, relative to baseline] (Grinder-Pedersen et al. 2003)

[Investigators at Kansas State University found higher total phenolic content in organic pac choi samples but no significant difference in lettuce and collards.] (Young et al. 2005)

[Italian researchers found higher anthocyanin levels in ripening conventionally grown syrah grapes compared to organic grapes. Anthocyanins are the antioxidants that impart red color to wine.] (Vian et al. 2006)

Cancer

While the link between vegetable consumption and cancer prevention—and the critical role of antioxidants in this phenomena—is increasingly understood, the question of whether or not cultivation method can have an impact on the anti-cancer properties of vegetables had been addressed only minimally until 2006 when a few more studies were published.

In Ren, Endo and Hayashi in 2001, 11 types of vegetable were sampled from a Japanese organic farm where no agricultural chemicals had been used for the previous 3 years. (The farm used organic fertilizers such as manure and compost as well as chitosan solution to treat infestations and molding.) A comparison group of the same 11 types was taken from a nearby conventional farm on the same day. In the experiment, supernatant from centrifuged juice extract from the vegetables was incubated with known mutagenic chemicals and standardized bacteria for 2 hours. The cultures were then measured to see how many bacterial colonies were prevented from undergoing genetic mutation in the presence of the vegetable extracts. The organic vegetables showed significantly more antimutagenic ability than the conventional vegetables, as summarized below (Ren et al. 2001):
Vegetables Mutagen Organic Veg Mutation Suppression Conventional Veg Mutation Suppression
Chinese cabbage, Carrot, Welsh onion, Qing-gen-cai 4-nitroquinoline oxide (4NQO) 37–93% 11–65%
Japanese radish, Green pepper, Welsh onion benzo(a)pyrene (BaP) 30–57% 5–30%
Spinach 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate
(Trp-P-2) 78% 49%

[Olsson et al (Sweden) took this type of research a step further and looked at the effect of strawberries on cultures of human colon cancer and breast cancer cells. They found that at high concentrations, extract from organically grown strawberries had increased antiproliferative effect on both cell types compared to conventionally grown strawberries]. (Olsson et al. 2006)

[Last year, Italian researchers used a similar methodology to study antioxidant effectiveness of red oranges on laboratory cultures of rat cadiomyocytes (heart tissue cells) and a human carcinoma cell line.  They concluded that phenol levels were higher in the organic oranges. Organic extracts were better able to inhibit the production of conjugated diene containing lipids and free radicals in the cell cultures.] (Tarozzi et al. 2006)