A collaborative study between the University of Helsinki, Natural Resources Institute Finland and Tampere University, has demonstrated that just one month of indoor gardening enhances immune regulation, can increase the bacterial diversity of the skin and is associated with higher levels of anti-inflammatory molecules in the blood.
It has previously been shown that contact with natural microbially-rich soil media alters the human microbiota, that is the 2 kg or so of microorganisms within each of us. Beneficial microbial exposure has decreased among people living in urban areas and they have distinct microbiota compositions compared to their rural counterparts.
Evidence suggests that home surroundings play a key role in determining microbiota-related health outcomes:
- Surroundings of forest and agricultural land during the first year of life are inversely associated with the risk of atopic sensitization and type 1 diabetes.
- Biodiverse and green living areas correlate with better respiratory health.
- Diverse garden vegetation and outdoor nature-related activities have been linked to health-related changes in the gut microbiota composition.
- Living in rural or farm-like conditions is directly associated with a diverse microbiota and a well-functioning immune system.
Participants in this research were recruited from the cities of Lahti (population > 120 000) and Hyvinkää (population > 45 000) in Finland. They had to be broadly healthy, with for example certain immune-mediated diseases excluded. They were randomised to either an intervention or placebo group and were asked to fill out questionnaires assessing their living conditions and lifestyle, including medication, food supplements, diet, outdoor activities and hobbies, and any contact with soil. Hand washing habits were also recorded. Samples from thirteen placebo and fifteen intervention group participants were used in the analyses. The participants’ ages ranged from 29 to 72.
Participants were provided with a planter, seeds, plants, and growing medium. The placebo group used horticultural peat, chosen because of its low bacterial diversity. The intervention group used the same horticultural peat mixed with a microbiologically rich compost-based mixture, containing composted materials such as tree bark, mulch, dung, deciduous leaf litter, peat, agricultural sludge, and Sphagnum moss.
Both groups were provided with the same seven crop species: lettuce, white mustard, radish, garlic, ginger, pea and fava bean. They were instructed to sow their seeds and daily tasks included both soil and dietary exposure: monitoring moisture levels by inserting a bare finger deep into the growing medium, watering, harvesting, and resowing. Blood samples, and skin swab samples for bacterial analyses, were collected at the beginning of the trial and at one month.
After one month, plasma anti-inflammatory cytokine IL-10 and skin bacterial diversity both increased in the intervention group. Since the diversity of bacteria increased in the intervention but not in the placebo group, the results suggest that handling a microbially-rich growing medium enriches the skin microbiota. Immune modulation was also enhanced in the intervention but not in the placebo group.
“The findings are significant, as urbanisation has led to a considerable increase in immune-mediated diseases, such as allergies, asthma and autoimmune diseases, generating high healthcare costs. We live too ‘cleanly’ in cities,” says Doctoral Researcher Mika Saarenpää. Microbial exposure can be increased easily and safely at home throughout the year. The space and financial investment required is minor. In the study, the gardening took place in regular flower boxes, while the plants cultivated, such as peas, beans, mustards and salads, came from the shop shelf. Changes were observed in only a month, but as the research subjects enjoyed the gardening, many of them announced that they would continue the activity and switch to outdoor gardening in the summer.
Noteworthy for gardeners is that this research suggests that peat, the most widely used growing medium in the world, does not appear to bring the health benefits associated with a medium mimicking diverse forest soil.
(Urban indoor gardening enhances immune regulation and diversifies skin microbiota — A placebo-controlled double-blinded intervention study. Environment International, May 2024.)
If an iron supplement has been recommended to you by a professional, then here are some useful guidelines for taking it. If you are unaware of these considerations, you won’t get the best value for money from your supplement and it may take longer than necessary for your iron levels to get back up to normal. 
Haem iron is found in meat, fish and poultry. It is the most easily absorbed form of dietary iron.
Non-haem iron is found in plant foods but also occurs in animal tissue. It is significantly less well absorbed than haem iron [1], so vegetarians and vegans have to be more vigilant when it comes to ensuring sufficient iron in their diets. Nevertheless, these foods are important components of a well-balanced diet.
Some components in our diets can inhibit iron uptake. These are phytates, polyphenols, calcium and animal protein from milk and eggs. Taking these in order, phytates are present in plant-based diets in foods such as whole wheat, oats, rice, black beans, pinto beans, kidney beans, soybeans, peanuts, lentils, walnuts, pine nuts, almonds, sesame seeds, potatoes, beetroot, turnips and carrots. Once again, these foods are important elements of a well-balanced diet.
Next on the list of inhibitors come polyphenols. These are found in some fruit, vegetables, red wine and teas including herbal teas. They offer many benefits including anti-inflammatory and anti-oxidant properties and positively should be part of your diet. They do however, inhibit iron absorption. This means don’t have black tea, coffee, cocoa, or herb teas like chamomile or peppermint (the common ones I found referenced in the research literature) at the same time as your iron supplement. Black tea appears the most inhibiting and red wine the least. The addition of milk to tea and coffee appears to make no significant difference.
Another common inhibitor is calcium. This seems to have a limited effect on haem and non-haem iron absorption, being taken up preferentially at the expense of the iron. In the diet as a whole, it is probably less of an issue, but it would seem sensible if you have also been recommended to take a calcium supplement for osteoporosis say, not to take it at the same time as your supplemental iron.
Finally, animal proteins such as milk and egg proteins, are also inhibitors of iron uptake, as is soy protein. It would follow that avoiding milk, eggs or sports protein supplements with your iron, would make sense.
Next we come to the two main enhancers of iron uptake: vitamin C and animal tissue. Vitamin C is able to reduce Fe3+ to Fe2+ (see [1] below). Let vitamin C be a trump card for you. It can counteract the unhelpful effects of all the inhibitors mentioned above and is a good supplement to take alongside your iron.
In vegetarian and vegan diets, fruit and vegetables rich in vitamin C can be used at every meal to enhance uptake of the non-haem iron in those meals. Kiwi fruit for example would be a good dessert. Connected with that though, be aware that cooking and storage can degrade vitamin C in food. This applies to freezing, and especially to the boiling of vegetables where vitamins C and B dissolve in the water which gets discarded.
Distinct from the animal-derived proteins mentioned above as inhibitors, animal tissue on the other hand is an enhancer of iron uptake. This includes meat, fish and poultry.
University-based authors in Malaysia have concluded that honey enhances cognition and memory, following a review of 34 studies on honey consumption, and the physical and/or psychological health of the brain. The studies, selected from an initial 330, were a combination of human and animal studies. Beneficial effects were reported in human subjects for mild cognitive impairment, dementia prevention and short-term memory.