To solve the given optimization problem and convert it into a symbolic representation along with Gurobi code, we'll first break down the variables and their corresponding natural language objects. Then, we will formulate the objective function and constraints symbolically.

### Symbolic Representation

Let's define the variables:
- $x_1$ for milligrams of vitamin B5
- $x_2$ for milligrams of magnesium
- $x_3$ for milligrams of potassium
- $x_4$ for milligrams of zinc

The objective function is to minimize: $2x_1 + 3x_2 + x_3 + 2x_4$

Constraints are as follows, but due to the extensive nature of the constraints provided in the problem description, we will directly implement them in the Gurobi code for clarity and accuracy. However, some key constraints include:
- Digestive support indices
- Immune support indices
- Kidney support indices
- Various combinations of these support indices with minimum or maximum requirements

### Gurobi Code Implementation

```python
from gurobipy import *

# Create a new model
m = Model("Optimization_Problem")

# Define the variables
x1 = m.addVar(lb=0, name="milligrams_of_vitamin_B5")
x2 = m.addVar(lb=0, name="milligrams_of_magnesium")
x3 = m.addVar(lb=0, name="milligrams_of_potassium")
x4 = m.addVar(lb=0, name="milligrams_of_zinc")

# Set the objective function
m.setObjective(2*x1 + 3*x2 + x3 + 2*x4, GRB.MINIMIZE)

# Define the constraints based on the given problem description
# Digestive support index constraints
m.addConstr(6*x1 + 3*x2 + 8*x3 + 7*x4 <= 168) # Total digestive support index constraint
m.addConstr(6*x1 + 8*x3 + 7*x4 >= 16) # Minimum digestive support from vitamin B5, potassium, and zinc
m.addConstr(3*x2 + 8*x3 + 7*x4 >= 36) # Minimum digestive support from magnesium, potassium, and zinc
m.addConstr(6*x1 + 3*x2 + 7*x4 >= 27) # Minimum digestive support from vitamin B5, magnesium, and zinc
m.addConstr(6*x1 + 3*x2 + 8*x3 + 7*x4 >= 35) # Total minimum digestive support index

# Immune support index constraints
m.addConstr(6*x1 + 13*x4 >= 29) # Minimum immune support from vitamin B5 and zinc
m.addConstr(8*x2 + 13*x4 >= 22) # Minimum immune support from magnesium and zinc
m.addConstr(8*x2 + 5*x3 >= 34) # Minimum immune support from magnesium and potassium
m.addConstr(6*x1 + 5*x3 + 13*x4 >= 37) # Minimum immune support from vitamin B5, potassium, and zinc

# Kidney support index constraints
m.addConstr(7*x3 + 8*x4 >= 29) # Minimum kidney support from potassium and zinc
m.addConstr(x1 + x2 + x3 + x4 >= 0) # Non-negativity constraint for all variables

# Additional constraints as per the problem description
m.addConstr(4*x2 - 5*x4 >= 0)
m.addConstr(9*x1 - 9*x2 >= 0)

# Upper bound constraints for digestive support indices
m.addConstr(3*x2 + 7*x4 <= 137) # Maximum digestive support from magnesium and zinc
m.addConstr(6*x1 + 3*x2 <= 112) # Maximum digestive support from vitamin B5 and magnesium

# Solve the model
m.optimize()

# Print the solution
for v in m.getVars():
    print('%s %g' % (v.varName, v.x))

print('Obj: %g' % m.objVal)
```