Climate-Smart Diet and Danish Resistance Against Spanish Flu in 1918 – Revised

“Age-specific” data concerning incident influenza rate, influenza

death rate and total death rate in Danish towns are attained from Figure 1 in [2]: Y-axis values (on logarithmic scale) were measured by ruler. First was measured distance between y-value 1 and y-value 100,000 ( = Power(10;5). It was 9.6 cm. Then was measured parameter values, e.g. of total number of deaths (Tot) as cm (x) of each month. Equation Tot = Power(10;x/(9.6/5)) gave the number of deaths. Similarly, were attained data for incident influenza rate and influenza death rate. Obviously because accurate diagnoses for mild incident influenza cases were not available, 'alii morbi epidemici' was used as an account for the influenza mortality [2] and gives freedom to use "flu" instead of "influenza" for mortality. It seems that all "incident influenza cases" were not caused by Spanish flu, because they existed every month before, between and after the epidemic. In the tables are used the same labels for incidence "influenza" as in [2], but in the text often the more realistic "flu".

Historical
Climate-Smart Diet: Commercial blockade placed Denmark in a very serious situation during The I World War [3]. Before blockade Denmark had imported more than half of her bread cereals and a very considerable amount of corn and oil cakes for the use of domestic animals [3]. Earlier butter was mainly exported, people used margarine and skimmed milk was given to pigs [5]. Since Apr 1917 committee of Hindhede begun to work with following consequences [3]: the stock of cattle was dropped by 35 % and number of pigs by 83 % [4], brandy distillation was stopped totally and the beer production was reduced by a half [3]. Principal foods were bran bread, barley porridge, potatoes, greens, milk, and some butter [3]. Bran bread was composed of rye (milled to 100 per cent), 24 % of barley meal (milled to 95 %) and all available wheat bran.
No wheat bran was used as fodder [3]. This procedure gave more than twice the amount of bread compared with alternative when rye had been milled to 70% [3]. Direct consumption of crops by humans saved nutritional energy ca 80 %. Perfect food restrictions were realized between Sept 30, 1917 andNov 1, 1918. ("By October 1917, food restrictions had become very severe" [3] and after October, 1918, it was not possible to continue the experiment "because of the epidemic of influenza" [3]. Statistically assessed "experimental year" in [3] occurred between Oct 1 of 1917 and 1918 (including Oct 1917 and Sept 1918) (Figure 1). During 1900-1916 the range of variation in total mortality of middle aged men in Copenhagen had been 7 %, but during "the experimental year" it was 34 % lower than the average in 1900-1916 [3]. "The death rate for women was also been lowered 17 per cent. "in" the four year period 1910-14." [3]. (Possibly "in" must be "to". 1910-1914, "four years" means period from Jan 1 to Jan 1?)

Result
The estimated, from [2] attained data, show that flu epidemic      This picture, as in this article in general, which represents "age-spesific", by population of 1920 weighted data [2], is giving more weight for middle-aged people, Tot.18 is 7 % above the mean of "age-spesific", Tot.16 & Tot.19 -as it seems to be). Paradox between high number of registered influenza cases and no change in total mortality is explained by changes in "Non-flu deaths" ( Figure 5).

Discussion on Statistics
Influenza epidemics affected seriously Danish towns in 1918-1920 (Figures 1,2,4). Spanish flu incidence was highest in Oct.18 and death-rate in Nov.18 (Figure 1), but lethality was highest in the springs 1919 and 1920 (2.2 -2.3%) opposite to Oct -Dec 1918 with 1.9% and Jul.18 -Sept. 18 (first wave of the flu) with 0.4%. ( Figure   3). Lower lethality in Oct -Dec 1918 can be dependent on the normal monthly variation in mortality [8], but other factors cannot be excluded. In USA highest "lethality rate" has been reported from Oct 18 [9], but it is possible that the term "lethality rate" has been used as synonym for death-rate, not in its scientific meaning [10] and tells more about the simultaneousness of the epidemic: one month difference with the maximum peaks in Denmark and USA. Monthly  [11] is not clearly seen in Figure 5.

Virtual Experiment
Hindhede describes that after the dietary changes in 1917 the principal foods were: bran bread, barley porridge, potatoes, greens, milk and some butter [3]. Shortly said: imported food was mainly replaced by the crops earlier given to pigs. "Hinhede" (supplementation) contained mainly potatoes, barley and wheat bran. In the following virtual experiment 50 % of the Finnish diet from the 1970's [12], which gives mineral element values per 10 MJ [13], was replaced by barley, potatoes and wheat bran. The protein amount (106.25 g) was attained by multiplying nitrogen (17 g) by The virtual "Hindhede" supplementation [16]

Discussion on Virtual Study
The surprisingly small change in protein and P content could be explained by high sugar consumption in 1976-77: 112.5 g/d, [17] resp a´ 117 kJ/g [n.15], total 1.9 MJ/d (19 %). (The study [12], including planning and analytical work, was performed in 1975-78, why only 1976 and 1977 are selected for determination of sugar consumption. This is higher than 100 g in [12] represented). Alcohol consumption, 13.6 g alcohol/d/capita [12], a´ 25 MJ/kg [18], which responds 3.4 E%, seems not to be on an average as important, if we assess mineral composition of food, because some alcoholic drinks contain mineral elements, too (e.g. beer). It seems that the possible effect of "Hindhede" supplementation was not based on low protein content as sometimes suggested [5]. Changes in fat consumption changed during the war: earlier butter was exported and Dänish people consumed margarine (without vitamin supplementation) [5]. Fat reduction was obviously not as great as caused by the above virtual replacement, because of commercial blockage butter export was not possible and cattle reduction was only 35% [4]. Ca content in the "Hindhede" (supplementation) per 10 MJ was low (260 g/d).
The high content in "replaced diet" (880 mg) was caused by the high Finnish Ca consumption [12]. Hindhede obviously had remarked, this when he wrote: "The people must first have bread, potatoes and cabbage in sufficient quantity, and then some milk. Meat is the last requirement to be met" [3]. Cabbage is rich in Ca [16].
Potato is rich in vitamin C and contains essential amino acids (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) per energy unit about 90 % of that of cereals (wheat, rye, barley) and about 1.5-fold lysine but 2/3 of methionine to that of the cereals [16]. Lysine is important because it is present only in limited amounts in plant proteins [19]. Hunger and obesity caused by lysine deficiency is better to treat by potato than cereals.
β-sitosterols with several benefits [20]. Important factors could be the other protective nutrients in the "Hindhede" supplementation: normal functions of the cells [21]. Structural properties of Si are obviously beneficial in CVD and musculoskeletal diseases [22] and generally in cellular protection. It is possible that soluble silicon or silicon compounds can protect against infectious diseases [23]. In water stress Si can increase potato yield and proline content [24], (proline content ca ad two-fold). Proline in an important part of milk tripeptides with ACE function [25]. about on the same level as next time after the CHD epidemic  in 1985 [26], although milk fat-% was obviously remarkably higher than today. One of the suggested causes for the increase in male CHD could have been reduced recycling of plant nutrients and the delay in Mg-fertilization [27], as well as in Si fertilization. Silicon content of human diets has been "about 20 to 50 mg/day with the lower values for animal-based diets and the higher values for plantbased diets" [28]. Benefits of Hindhede diet have been possibly higher, if we knew the number of subclinical (symptomless) Spanish flu infections, which was obviously higher in Denmark than in Sweden, supposed by the higher population density [2].
Explanations on different resistance against infectious diseases (e.g. covid-19) [29] are suggested to be studied by different dietary habits, e.g. by different silicon availability, in public health via food balance sheets of FAOSTAT or in indual cases via serum Si values.
Interesting mineral element could be even tin, which is associated with thymic functions [30]. If we remember cabbage and other "greens", Hindhede diet seems to be more climate-smart, economic and ecologic than newer recommendations [31]. Renaissance of potatoes, possibly by selected cultivars, is expected.

Conclusion
Climate-smart diet associated with slightly lower non-flu mortality and possibly lethality of Spanish flu in Danish towns during 1916-21. Discussion on roles of potatoes and silicon is suggested.