---
title: "Human nutrition"
chunk: 16/20
source: "https://en.wikipedia.org/wiki/Human_nutrition"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:55:25.210940+00:00"
instance: "kb-cron"
---

==== Elderly Nutrition: Zinc ====
Zinc is a vital micronutrient that plays a crucial role in enzymatic catabolism, immune cell function, DNA synthesis, and various micronutrient metabolisms. In the elderly, low serum zinc levels have been reported, which weakens the immune system, making them more susceptible to infections and increasing their risk of morbidity. Aging impairs T cell function, particularly due to zinc deficiency, and the reduced synthesis of metallothionein disrupts zinc balance in the gut and other tissues. This deficiency is primarily due to inadequate dietary zinc intake, compounded by factors such as poor mastication, oral health issues, medication use that interferes with absorption, and psychosocial factors that limit food intake. Additionally, epigenetic changes like DNA methylation may impair zinc transporters, leading to decreased zinc absorption as people age. Structural changes in the gut, including altered villus shape, mitochondrial changes, crypt elongation, collagen alterations, and increased cell replication time in the crypts, also significantly affect zinc absorption in the elderly.
The recommended daily allowance of zinc is 11 mg for older men and 8 mg for older women, with an upper tolerable limit of 25–40 mg per day, including both dietary and supplemental sources. However, individuals over 60 often consume less than 50% of the recommended zinc intake, which is crucial for proper body function. Data from the Third Health and Nutrition Survey in the United States revealed that only 42.5% of adults over 71 years old met adequate zinc intake levels, with many suffering from zinc deficiency. To reach the upper tolerable limit of 40 mg per day, zinc intake from both food and supplements must be considered to help normalize serum zinc levels in deficient elderly individuals. Dietary sources such as seafood, poultry, red meat, beans, fortified cereals, whole grains, nuts, and dairy products are beneficial for maintaining adequate zinc levels, though absorption is higher from animal proteins than plant-based sources.

==== Elderly Nutrition: Vitamin-B Complex ====
The Vitamin-B complex, which includes eight water-soluble vitamins, plays a crucial role in maintaining cellular function and preventing brain atrophy. Among the elderly, deficiencies in vitamins B12, B6, and folate are linked to cognitive decline and depressive symptoms.
The Recommended Dietary Allowance (RDA) for vitamin B12 is 0.9-2.4 μg/day, while the estimated average requirement in the U.S. and Canada is 0.7-2 μg/day. Elderly individuals with plasma vitamin B12 levels below 148 pmol/L are considered severely deficient, and those with levels between 148 and 221 pmol/L are marginally deficient. A deficiency in these B-vitamins, particularly B6, B12, and folate, is associated with elevated homocysteine levels, which increase the risk of alzheimer's disease and dementia. Increased intake of these vitamins can lower homocysteine levels and reduce the risk of these conditions. According to the National Health and Nutrition Examination Survey, about 6% of elderly Americans over 70 are severely deficient in vitamin B12, and more than 20% of those over 60 are mildly deficient. This deficiency is often due to insufficient food intake and malabsorption caused by degenerative digestive conditions, as indicated by elevated plasma gastrin levels in older adults. The deficiency of vitamin B6 among institutionalized elderly in Europe ranges from below 1% to 75%. B-vitamins are primarily found in animal-based foods, making deficiencies more common among those with limited animal food intake due to cultural, religious, or economic reasons. For vegetarians, fortified foods can be a viable alternative to ensure adequate vitamin B12 levels, especially when reducing laxative use to improve absorption.

==== Elderly Nutrition: Calcium & Vitamin D3 ====
Aging is often marked by a decline in bone mineral density, leading to an increased risk of osteoporotic fractures and reduced mobility, especially among elderly women. Women experience greater bone loss, around 2-3% per year, particularly after menopause due to estrogen deficiency. This deficiency reduces intestinal calcium absorption, decreases calcium reabsorption by the kidneys, and increases parathyroid hormone secretion, all contributing to bone resorption. Additionally, vitamin D3 deficiency, common in older adults due to reduced skin synthesis and limited sun exposure, further disrupts calcium homeostasis by decreasing intestinal absorption of calcium. As kidney function declines with age, the conversion of vitamin D3 to its active form is impaired, exacerbating the deficiency.
Serum 25(OH)D levels below 50 nmol/L are linked to muscle weakness and reduced physical function, while levels below 25-30 nmol/L increase the risk of falls and fractures. Older adults typically consume less calcium, around 600 mg/day, which heightens their susceptibility to fractures. For optimal bone health, a calcium intake of 1000–1200 mg/day is recommended, along with 800 IU/day of vitamin D3 for those with adequate sun exposure, and up to 2000 IU/day for those with limited sun exposure or obesity. However, dietary factors like phytates, oxalates, tannins, and high sodium can impair calcium absorption and retention, underscoring the need to maintain sufficient levels of both calcium and vitamin D3 through diet or supplementation to reduce the risk of pathologic fractures.